platform/x86: portwell-ec: Add GPIO and WDT driver for Portwell EC

platform/x86: portwell-ec: Add GPIO and WDT driver for Portwell EC

Adds a driver for the ITE Embedded Controller (EC) on Portwell boards.
It integrates with the Linux GPIO and watchdog subsystems to provide:

- Control/monitoring of up to 8 EC GPIO pins.
- Hardware watchdog timer with 1-255 second timeouts.

The driver communicates with the EC via I/O port 0xe300 and identifies
the hardware by the "PWG" firmware signature. This enables enhanced
system management for Portwell embedded/industrial platforms.

Signed-off-by: Yen-Chi Huang <jesse.huang@portwell.com.tw>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/a04be962-b207-4085-af5b-523f59bffcbc@portwell.com.tw
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>