drivers/gpio/cs5535-gpio.c: add some additional cs5535-specific GPIO functionality

This adds (well, re-adds actually) handling for events/IRQs through cs5535
GPIOs.  In the wild and wooly world of CS5535, setup_event() is for
assigning an IRQ to a GPIO filter/event pair, and set_irq() sets up the
pair to trigger IRQs.

These should really only be used in highly platform-specific drivers (such
as OLPC's DCON driver).  Sadly, because set_irq() uses MSRs, this causes
the driver to become X86-specific.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Daniel Drake <dsd@laptop.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>