gpio: add interrupt handling capability to max732x

gpio: add interrupt handling capability to max732x

Most of the GPIO expanders supported by the max732x driver have interrupt
generation capability by reporting changes on input pins through an INT#
pin.  This patch implements the irq_chip functionnality (edge detection
only).

Signed-off-by: Marc Zyngier <[email protected]>
Cc: Eric Miao <[email protected]>
Cc: Jebediah Huang <[email protected]>
Cc: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>