MXC arch: Add gpio support for the whole platform

This patch bases on the one from Daniel Mack. The most important change to
Daniel's patch is to be more generic. This gpio routine supports at least
the i.MX27 and i.MX31 processors.

Signed-off-by: Juergen Beisert <j.beisert@pengutronix.de>
Acked-by: Daniel Mack <daniel@caiaq.de>