[ARM] pxa/cm-x300: update the memory fixup.

CM-X300 bootloader passes DRAM configuration information in ATAGS,
however, the first memory bank is reported at actual physical address 0x8000000.
Use the configuration information supplied by the bootloader and
cope with the necessity to have PHYS_ADDR=0xa0000000.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>