platform/x86: Support for EC-connected GPIOs for identify LED/button on Barco P50 board

Add a driver providing access to the GPIOs for the identify button and led
present on Barco P50 board, based on the pcengines-apuv2.c driver.

There is unfortunately no suitable ACPI entry for the EC communication
interface, so instead bind to boards with "P50" as their DMI product family
and hard code the I/O port number (0x299).

The driver also hooks up the leds-gpio and gpio-keys-polled drivers to the
GPIOs, so they are finally exposed as:

LED:
/sys/class/leds/identify

Button: (/proc/bus/input/devices)
I: Bus=0019 Vendor=0001 Product=0001 Version=0100
N: Name="identify"
P: Phys=gpio-keys-polled/input0
S: Sysfs=/devices/platform/barco-p50-gpio/gpio-keys-polled/input/input10
U: Uniq=
H: Handlers=event10
B: PROP=0
B: EV=3
B: KEY=1000000 0 0 0 0 0 0

Signed-off-by: Santosh Kumar Yadav <santoshkumar.yadav@barco.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Link: https://lore.kernel.org/r/20211020123634.2638-1-peter@korsgaard.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>