Most of the GPIO expanders controlled by the pca953x driver are able to
report changes on the input pins through an *INT pin.

This patch implements the irq_chip functionality (edge detection only).

The driver has been tested on an Arcom Zeus.

[akpm@linux-foundation.org: the compiler does inlining for us nowadays]
Signed-off-by: NMarc Zyngier <maz@misterjones.org>
Cc: Eric Miao <eric.y.miao@gmail.com>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Nate Case <ncase@xes-inc.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>