powerpc/5200: Bugfix for PCI mapping of memory and IMMR

This patch ensures that memory gets properly mapped into the PCI
address space.  Without this patch, the memory window BAR is left
at whatever value happened to be loaded into the BAR when Linux
was booted.  Without this patch, memory could end up getting mapped
at any of the 1G address boundaries instead of at '0' where Linux
expects it.

Similarly, this patch also ensures that the internally memory mapped
registers (IMMR) are mapped to the correct PCI address range.

Without this patch, PCI appears to work correctly until a PCI
device is inserted which DMAs into memory.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Wolfram Sang <w.sang@pengutronix.de>