ARM: imx: use __iomem pointers for MMIO

ARM is moving to stricter checks on readl/write functions,
so we need to use the correct types everywhere.

This found a bug in mach-armadillo5x0.c, where we attempt mmio
on the MXC_CCM_RCSR address that is currently defined to 0xc
and consequently causes an illegal address access.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Shawn Guo <shawn.guo@linaro.org>