dt-bindings: input: matrix_keypad: convert to YAML

Convert the gpio-matrix-keypad bindings from text to DT schema.

Signed-off-by: Markus Burri <markus.burri@mt.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Manuel Traut <manuel.traut@mt.com>
Link: https://lore.kernel.org/r/20250110054906.354296-4-markus.burri@mt.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>