imx51: fix iomux configuration

- ALT0 is used to set GPIO mode of GPIO_1_{2,3,4,5,6,7,8,9} but it's ALT1
for GPIO_1_{0,1}.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>