ARM: imx: Modify IMX_IO_P2V macro

A change is needed in the IMX_IO_P2V macro to allow all imx5 platforms
to use common definitions when accessing registers of peripherals on
the AIPS2 bus.  With this change, IMX_IO_P2V(MX50_AIPS2_BASE_ADDR) ==
IMX_IO_P2V(MX51_AIPS2_BASE_ADDR) == IMX_IO_P2V(MX53_AIPS2_BASE_ADDR).

This change was tested for mapping conflicts using the iop2v script
found at git://git.pengutronix.de/git/ukl/imx-iop2v.git

 and by
performing a bootup of a default build using imx_v6_v7_defconfig
on a imx51 babbage board and imx53 loco board.  The comments were
modified to reflect the output given by the script which shows the
virtual address mappings.

Signed-off-by: Robert Lee <rob.lee@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>