reserving RAM in the bus_mem extent map. Problem pointed
out by Artur Grabowski.
- Work around a slightly annoying bit of behavior exhibited by
the UP1000 firmware. The UP1000 firmware reports the space
consumed by the "ISA hole" in the same MDDT entry as two
chunks of RAM (on either side of the hole) used by the PALcode,
all as one "reserved for PALcode" chunk. We must take this
into account when reserving RAM in the bus_mem extent map.
the `get window' method ends up with the wrong physical address to
pass onto userspace (which wants to mmap the space).
Compensate by adding a CHIP_PHYSADDR() macro which un-hacks the address
suitably for mapping with other-than-KSEG.