ARM: imx: fix TLB missing of IOMUXC base address during suspend

After the suspend routine running in OCRAM puts DDR into self-refresh,
it will access IOMUXC block to float DDR IO for power saving.  A TLB
missing of IOMUXC base address may happen in this case, and triggers an
access to DDR, and thus hangs the system.

The failure is discovered by running suspend/resume on a Cubox-i board.
Though the issue is not Cubox-i specific, it can be hit the on the board
quite easily with the 3.15 or 3.16 kernel.

Fix the issue with a dummy access to IOMUXC block at the beginning of
suspend routine, so that the address translation can be filled into TLB
before DDR is put into self-refresh.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Cc: <stable@vger.kernel.org>
Acked-by: Anson Huang <Anson.Huang@freescale.com>