Added a PIXIS_BASE_PHYS for use as the physical address and maintain
PIXIS_BASE as the virtual address of the PIXIS fpga registers.

This allows us to deal with 36-bit phys on these boards in the future.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Acked-by: NAndy Fleming <afleming@freescale.com>