dt-bindings: gpio: Add a header file for Amlogic Meson S4

Add a new dt-binding header file which documents the detail pin names.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Qianggui Song <qianggui.song@amlogic.com>
Link: https://lore.kernel.org/r/20220113031044.2665-3-qianggui.song@amlogic.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>