dt-bindings: arm: amlogic: Add support for GXL S905W and the P281 boa…

…rd - WiP

S905W SoC is another SoC from the GXL family. It is a cost-reduced
version of the S905X SoC. The following differences are known:
- S905W supports HDMI resolutions up to 4k@30fps (while S905X support
  resolutions up to 4k@60fps)
- the built-in video decoders of S905W decode up to 4k@30fps (while
  S905X supports decoding up to 4k@60fps)
- CPU speed on S905W is limited to 1.2GHz (compared to 1.5GHz on S905X)
- the DRAM interface on S905W is limited to 16-bit (GXL supports both,
  16-bit and 32-bit)

The P281 is a development board from Amlogic which uses the S905W SoC.
It uses the same PCB layout as the S905D P231 board.

TODO:
- pin-compatible???
- max GPU frequency is 650M???

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Documentation/devicetree/bindings/arm/amlogic.txt

@@ -37,6 +37,10 @@ Boards with the Amlogic Meson GXL S905D SoC shall have the following properties:
   Required root node property:
     compatible: "amlogic,s905d", "amlogic,meson-gxl";
 
+Boards with the Amlogic Meson GXL S905W SoC shall have the following properties:
+  Required root node property:
+    compatible: "amlogic,s905w", "amlogic,meson-gxl";
+
 Boards with the Amlogic Meson GXM S912 SoC shall have the following properties:
   Required root node property:
     compatible: "amlogic,s912", "amlogic,meson-gxm";
@@ -73,6 +77,8 @@ Board compatible values (alphabetically, grouped by SoC):
   - "amlogic,p230" (Meson gxl s905d)
   - "amlogic,p231" (Meson gxl s905d)
 
+  - "amlogic,p281" (Meson gxl s905w)
+
   - "amlogic,q200" (Meson gxm s912)
   - "amlogic,q201" (Meson gxm s912)
   - "khadas,vim2" (Meson gxm s912)