docs: Move the HTE documentation to driver-api/

The hardware timestamp engine documentation is driver API material, and
really belongs in the driver-API book; move it there.

Cc: Thierry Reding <treding@nvidia.com>
Acked-by: Dipen Patel <dipenp@nvidia.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-api/index.rst

@@ -108,6 +108,7 @@ available subsections can be seen below.
    xilinx/index
    xillybus
    zorro
+   hte/index
 
 .. only::  subproject and html
 

Documentation/index.rst

@@ -137,7 +137,6 @@ needed).
    scheduler/index
    mhi/index
    peci/index
-   hte/index
 
 Architecture-agnostic documentation
 -----------------------------------

MAINTAINERS

@@ -9081,7 +9081,7 @@ HTE SUBSYSTEM
 M:	Dipen Patel <dipenp@nvidia.com>
 S:	Maintained
 F:	Documentation/devicetree/bindings/timestamp/
-F:	Documentation/hte/
+F:	Documentation/driver-api/hte/
 F:	drivers/hte/
 F:	include/linux/hte.h