RT1718S is an i2c-based TCPC chip that supports 3 additional GPIOs.
The pins can be used for USB-C operations e.g. handling FRS, but they
can also work as usual GPIOs.
Add a driver for the RT1718S GPIO and a handler for an alert signal from
the chip. The handler reads the alert register once asserted and calls
the GPIO interrupt handler if needed(Vendor-defined alert).
gpio_rt1718s.c file and "richtek,rt1718s" node collect common properties
and data for all RS1718S functionalities. The file can be extended for
TCPC driver. rt1718s.h file also defines inline functions with i2c
operations common for all drivers. The common header and source files
can be moved to tcpc directories once the tcpc driver is added since it
is the main functionality.
Signed-off-by: Dawid Niedzwiecki <dn@semihalf.com>
