cros-ec-keyboard: Synchronize DT binding from linux

cros-ec-keyboard: Synchronize DT binding from linux

The ChromeOS EC keyboard is used by various different chromebooks. Peach
pi being the third board in the u-boot tree to use it (snow and peach
pit the other two). Rather then embedding the same big DT node in the
peach-pi DT again, copy the dtsi snippit & bindings documentation from
linux and include it in all 3 boards.

This slightly changes the dt bindings in u-boot:
  * google,key-rows becomes keypad,num-rows
  * google,key-colums becomes keypad,num-colums
  * google,repeat-delay-ms and google,repeat-rate-ms are no longer used
    and replaced by hardcoded values (similar to tegra kbc)

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>