ARM: dts: imx28: add pinmuxing for mmc1

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[ukl: rebase from ancient kernel version]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>