gpio: mpfs: Add interrupt support

gpio: mpfs: Add interrupt support

Add support for interrupts to the PolarFire SoC GPIO driver. Each GPIO
has an independent interrupt that is wired to an interrupt mux that sits
between the controllers and the PLIC. The SoC has more GPIO lines than
connections from the mux to the PLIC, so some GPIOs must share PLIC
interrupts. The configuration is not static and is set at runtime,
conventionally by the platform's firmware. CoreGPIO, the version
intended for use in the FPGA fabric has two interrupt output ports, one
is IO_NUM bits wide, as is used in the hardened cores, and the other is
a single bit with all lines ORed together.

Acked-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>