gpio: mt7621: fix interrupt banks mapping on gpio chips

gpio: mt7621: fix interrupt banks mapping on gpio chips

The GPIO controller's registers are organized as sets of eight 32-bit
registers with each set controlling a bank of up to 32 pins. A single
interrupt is shared for all of the banks handled by the controller.
The driver implements this using three gpio chip instances every one
with its own irq chip. Every single pin can generate interrupts having
a total of 96 possible interrupts here. It looks like there is a problem
with interrupts being properly mapped to the gpio bank using this solution.
This problem report is in the following lore's link [0].

Device tree is using two cells for this, so only the interrupt pin and the
interrupt type are described there. Changing to have three cells to setup
also the bank and implement 'of_node_instance_match()' would also work but
this would be an ABI breakage and also a bit incoherent since gpios itself
are also using two cells and properly mapped in desired bank using through
its pin number on 'of_xlate()'.

That said, register a linear IRQ domain of the total of 96 interrupts shared
with the three gpio chip instances so the bank and the interrupt is properly
decoded and devices using gpio IRQs properly work.

[0]: https://lore.kernel.org/linux-gpio/CAAMcf8C_A9dJ_v4QRKtb9eGNOpJ7BZNOGsFP4i2WFOZxOVBPnQ@mail.gmail.com/T/#u

Fixes: 4ba9c3afda41 ("gpio: mt7621: Add a driver for MT7621")
Co-developed-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: Vicente Bergas <vicencb@gmail.com>
Tested-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://patch.msgid.link/20260609031118.2275735-1-sergio.paracuellos@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>