gpio: kempld: Implement the interrupt controller

gpio: kempld: Implement the interrupt controller

Add a GPIO IRQ chip implementation for the kempld GPIO controller. Of
note is only how the parent IRQ is obtained.

The IRQ for the GPIO controller can be configured in the BIOS, along
with the IRQ for the I2C controller. These IRQ are returned by ACPI
but this information is only usable if both IRQ are configured. When
only one is configured, only one is returned making it impossible to
know which one it is.

Luckily the BIOS will set the configured IRQ in the PLD registers, so
it can be read from there instead, and that also work on platforms
without ACPI.

The vendor driver allowed to override the IRQ using a module
parameters, so there are boards in field which used this parameter
instead of properly configuring the BIOS. This implementation provides
this as well for compatibility.

Signed-off-by: Alban Bedel <alban.bedel@lht.dlh.de>
Link: https://patch.msgid.link/20260311143120.2179347-5-alban.bedel@lht.dlh.de
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>