Implement more of the PPC32 Pattern ISel:

Implement more of the PPC32 Pattern ISel:
1) dynamic stack alloc
2) loads
3) shifts
4) subtract
5) immediate form of add, and, or, xor
6) change flag from -pattern-isel to -enable-ppc-pattern-isel

Remove dead arguments from getGlobalBaseReg in the simple ISel

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20810 91177308-0d34-0410-b5e6-96231b3b80d8