Better codegen of binary integer ops with 32 bit immediate operands.

This transformation fires a few dozen times across the testsuite.

For example, int test2(int X) { return X ^ 0x0FF00FF0; }
Old:
_test2:
        lis r2, 4080
        ori r2, r2, 4080
        xor r3, r3, r2
        blr

New:
_test2:
        xoris r3, r3, 4080
        xori r3, r3, 4080
        blr

llvm-svn: 17004