bcma: switch GPIO portions to use GPIOLIB_IRQCHIP

This switches the BCMA GPIO driver to use GPIOLIB_IRQCHIP to
handle its interrupts instead of rolling its own copy of the
irqdomain handling etc.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>