dt-bindings: pinctrl: Add bindings for Intel Keembay pinctrl driver

Add Device Tree bindings documentation for Intel Keem Bay
SoC's pin controller.
Add entry for INTEL Keem Bay pinctrl driver in MAINTAINERS file

Co-developed-by: Vineetha G. Jaya Kumaran <vineetha.g.jaya.kumaran@intel.com>
Signed-off-by: Vineetha G. Jaya Kumaran <vineetha.g.jaya.kumaran@intel.com>
Co-developed-by: Vijayakannan Ayyathurai <vijayakannan.ayyathurai@intel.com>
Signed-off-by: Vijayakannan Ayyathurai <vijayakannan.ayyathurai@intel.com>
Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@intel.com>
Acked-by: Mark Gross <mgross@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210806142527.29113-2-lakshmi.sowjanya.d@intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>