dt-bindings: pinctrl: convert pinctrl-mcp23s08.txt to yaml format

dt-bindings: pinctrl: convert pinctrl-mcp23s08.txt to yaml format

YAML binding file provides the conversion of the original text-based
binding for the pinctrl-mcp23s08 to microchip,mcp23s08.yaml.

following compatible strings using the deprecated mcp prefix have been
removed from this binding:

- mcp,mcp23s08
- mcp,mcp23s17
- mcp,mcp23008
- mcp,mcp23017

Signed-off-by: Himanshu Bhavani <himanshu.bhavani@siliconsignals.io>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/20241028063939.6276-1-himanshu.bhavani@siliconsignals.io
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>