[ARM] 2950/1: i.MX gpio setup function

Patch from Sascha Hauer

Current implementation of imx_gpio_mode does not allow to
configure all alternate routing possibilities of the i.MX. With
this patch every bit in the gpio setup registers has a
corresponding bit in the gpio_mode parameter, so every routing
should be possible now.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>