[ARM] 3371/1: ep93xx: gpio support

Patch from Lennert Buytenhek

Add support for setting the direction of and getting/setting the
value of the 64 GPIO lines.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>