pinctrl: bcm2835: Workaround for edge IRQ loss

It has been observed that edge events can be lost when GPIO edges occur
close to each other. Investigation suggests this is due to a hardware
bug, although no mechanism has been identified.

Work around the event loss by moving the IRQ acknowledgement into the
main ISR, adding missing events by explicit level-change detection.

See: https://forums.raspberrypi.com/viewtopic.php?t=350295



Signed-off-by: Phil Elwell <phil@raspberrypi.com>