uninorth.c: add support for UniNorth kMacRISCPCIAddressSelect (0x48) register

uninorth.c: add support for UniNorth kMacRISCPCIAddressSelect (0x48) register

Darwin/OS X use the undocumented kMacRISCPCIAddressSelect (0x48) to
configure PCI memory space size for mac99 machines. Without this
register, warnings similar to below are emitted to the console during boot:

AppleMacRiscPCI: bad range 2(80000000:01000000)
AppleMacRiscPCI: bad range 2(81000000:00001000)
AppleMacRiscPCI: bad range 2(81080000:00080000)

Based upon the algorithm in Darwin's AppleMacRiscPCI.cpp driver, set the
kMacRISCPCIAddressSelect register so that Darwin considers the PCI
memory space to be at 0x80000000 (size 0x10000000) which matches that
currently used by QEMU and OpenBIOS.

Signed-off-by: John Arbuckle <programmingkidx@gmail.com>
Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
[commit message and comment revised as suggested by Mark Cave-Ayland]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>