gpio: mt7621: use the generic GPIO chip lock for IRQ handling

gpio: mt7621: use the generic GPIO chip lock for IRQ handling

This driver uses its own spinlock in interrupt routines while the
generic GPIO chip callbacks use a separate one. This is, of course, racy
so use the fact that the lock in generic GPIO chip is also a spinlock and
convert the interrupt handling functions in this module to using the
provided generic GPIO chip locking API.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250910-gpio-mmio-gpio-conv-part4-v2-9-f3d1a4c57124@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>