Microchip: MEC172x: Update pinmux driver

Update the Microchip XEC pinmux driver to use system I/O
routine for read/write of registers instead of direct use
of volatile and CMSIS defines. Add GPIO port number to
bindings instead of using hard coded value from chip headers.
Modify SoC DTSI pinmux syntax, requires "pinmux: pinumx {..."
or the DT macros will not work. Since pinmux is used by MEC152x
we update its chip pinmux DT.

Signed-off-by: Scott Worley <scott.worley@microchip.com>