dt-bindings: input: convert syna,rmi4 to DT schema

Convert the bindings for Synaptics RMI4 bus and devices to DT schema.
Changes during conversion:
1. Add reset-gpios already used in DTS and mentioned by RMI4
   specification.
2. Do not require address/size cells, because without functions
   (children) they aren't really needed.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230728165054.88678-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>

Author: krzk