docs: dt: Make 'Devicetree' wording more consistent

There's a variety of ways 'Devicetree' has been written. This is most
evident in the documentation build contents where we have 'Device Tree',
'DeviceTree', etc. The DT spec has somewhat standardized on
'Devicetree', so let's use that.

Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210325164713.1296407-5-robh@kernel.org

Documentation/devicetree/bindings/submitting-patches.rst

 .. SPDX-License-Identifier: GPL-2.0
 
 ==========================================
-Submitting devicetree (DT) binding patches
+Submitting Devicetree (DT) binding patches
 ==========================================
 
 I. For patch submitters

Documentation/devicetree/changesets.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-=============
-DT Changesets
-=============
+=====================
+Devicetree Changesets
+=====================
 
-A DT changeset is a method which allows one to apply changes
+A Devicetree changeset is a method which allows one to apply changes
 in the live tree in such a way that either the full set of changes
 will be applied, or none of them will be. If an error occurs partway
 through applying the changeset, then the tree will be rolled back to the

Documentation/devicetree/dynamic-resolution-notes.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-==================================
-Device Tree Dynamic Resolver Notes
-==================================
+=================================
+Devicetree Dynamic Resolver Notes
+=================================
 
 This document describes the implementation of the in-kernel
-Device Tree resolver, residing in drivers/of/resolver.c
+DeviceTree resolver, residing in drivers/of/resolver.c
 
 How the resolver works
 ----------------------

Documentation/devicetree/index.rst

 .. SPDX-License-Identifier: GPL-2.0
 
 =============================
-Open Firmware and Device Tree
+Open Firmware and Devicetree
 =============================
 
 .. toctree::

Documentation/devicetree/of_unittest.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-==================================
-Open Firmware Device Tree Unittest
-==================================
+=================================
+Open Firmware Devicetree Unittest
+=================================
 
 Author: Gaurav Minocha <gaurav.minocha.os@gmail.com>
 

Documentation/devicetree/overlay-notes.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-=========================
-Device Tree Overlay Notes
-=========================
+========================
+Devicetree Overlay Notes
+========================
 
 This document describes the implementation of the in-kernel
 device tree overlay functionality residing in drivers/of/overlay.c and is a
@@ -11,7 +11,7 @@ companion document to Documentation/devicetree/dynamic-resolution-notes.rst[1]
 How overlays work
 -----------------
 
-A Device Tree's overlay purpose is to modify the kernel's live tree, and
+A Devicetree's overlay purpose is to modify the kernel's live tree, and
 have the modification affecting the state of the kernel in a way that
 is reflecting the changes.
 Since the kernel mainly deals with devices, any new device node that result

Documentation/devicetree/usage-model.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-=========================
-Linux and the Device Tree
-=========================
+========================
+Linux and the Devicetree
+========================
 
 The Linux usage model for device tree data
 
@@ -14,7 +14,7 @@ at devicetree.org\ [1]_.
 
 .. [1] https://www.devicetree.org/specifications/
 
-The "Open Firmware Device Tree", or simply Device Tree (DT), is a data
+The "Open Firmware Device Tree", or simply Devicetree (DT), is a data
 structure and language for describing hardware.  More specifically, it
 is a description of hardware that is readable by an operating system
 so that the operating system doesn't need to hard code details of the

Documentation/devicetree/writing-schema.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-Writing DeviceTree Bindings in json-schema
+Writing Devicetree Bindings in json-schema
 ==========================================
 
 Devicetree bindings are written using json-schema vocabulary. Schema files are