ASoC: dt-bindings: maxim,max9759: Convert to DT schema.

Convert Maxim MAX9759 Speaker Amplifier bindings to DT schema.
Add missing gpio header file into examples section

Signed-off-by: Otabek Nazrullaev <otabeknazrullaev1998@gmail.com>
Cc: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230315173404.7215-1-otabeknazrullaev1998@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>