mfd: Add NCT38xx multi-function driver

The Nuvoton NCT38xx is a multi-function device providing a TCPC
controller and a I/O expander (GPIO driver).  Add a multi-function
driver to manage exclusive access to the device.

Tested with "twister -T tests/drivers/build_all/gpio".

Signed-off-by: Keith Short <keithshort@google.com>