pinctrl: bcm2835: Fix ints for GPIOs 28-31 & 46-53

Contrary to the documentation, the BCM2835 GPIO controller actually
has four interrupt lines - one each for the three IRQ groups and one
common. Confusingly, the GPIO interrupt groups don't correspond
directly with the GPIO control banks. Instead, GPIOs 0-27 generate IRQ
GPIO0, 28-45 IRQ GPIO1 and 46-53 IRQ GPIO2.

Awkwardly, the GPIOs for IRQ GPIO1 straddle two 32-entry GPIO banks,
so split out a function to process the interrupts for a single GPIO
bank.

Cc: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>