bcma: gpio: Convert to immutable gpio irqchip

This switches the BCMA gpio irqchip to be immutable. The GPIO subsystem plays
tricks on the irqchip structures, and we're fixing it one driver at a time. See
merge commit 4bde53ab ("Merge branch irq/gpio-immutable into
irq/irqchip-next") for all the details.

Tested on the D-Link DWL-6810AP.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221012192348.2234478-1-linus.walleij@linaro.org