ARM: mach-imx: mm-imx5: Retrieve iomuxc base address from dt

As mx53 is a dt-only SoC, we should retrieve the iomuxc base address from the
device tree, instead of using the old MX53_IO_ADDRESS method.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>