Compile test/CodeGen/PowerPC/LargeAbsoluteAddr.ll to:

_test:
        lis r2, 743
        li r3, 0
        stw r3, 32751(r2)
        blr

instead of:

_test:
        li r2, 0
        stw r2, 32751(48693248)
        blr

Implement support for ppc64 as well, allowing it to produce better code.

llvm-svn: 34371