dt-bindings: Create DT bindings for SATA controllers

I need to create subnodes for drives connected to SATA
host controllers, and this needs to be supported
generally, so create a common YAML binding for
"sata" that will support subnodes with ports.

This has been designed as a subset of
ata/ahci-platform.txt with the bare essentials and
should be possible to extend or superset to cover the
common bindings.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
[robh: fixup sata-port unit-address pattern]
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/ata/sata-common.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/ata/sata-common.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Common Properties for Serial AT attachment (SATA) controllers
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: |
+  This document defines device tree properties common to most Serial
+  AT attachment (SATA) storage devices. It doesn't constitute a device tree
+  binding specification by itself but is meant to be referenced by device
+  tree bindings.
+
+  The SATA controller-specific device tree bindings are responsible for
+  defining whether each property is required or optional.
+
+properties:
+  $nodename:
+    pattern: "^sata(@.*)?$"
+    description:
+      Specifies the host controller node. SATA host controller nodes are named
+      "sata"
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^sata-port@[0-9a-e]$":
+    description: |
+      DT nodes for ports connected on the SATA host. The SATA port
+      nodes will be named "sata-port".
+    type: object
+
+    properties:
+      reg:
+        minimum: 0
+        maximum: 14
+        description:
+          The ID number of the drive port SATA can potentially use a port
+          multiplier making it possible to connect up to 15 disks to a single
+          SATA port.
+
+...