mpr/mps crash badly. Part of the stability added use of atomic64 functions not
present on 32-bit powerpc. Merge the part that removes mps from the build
on this tier 2 platform. Working mpr/mps in 12 and 12.1 on our tier 1 platforms
is more important.
Remove the mps driver from powerpc 32bit GENERIC, and don't build it and mpr as a module for powerpc or mips. An upcoming commit will cause these drivers to rely on the presence of 64bit atomic operations. Discussed with jhibbits.