Add ori reg, reg, 0 as a move instruction. This can be generated from

Add ori reg, reg, 0 as a move instruction.  This can be generated from
loading a 32bit constant into a register whose low halfword is all zeroes.

We now omit the ori after the lis for the following C code:

int bar(int y) { return y * 0x00F0000; }

_bar:
.LBB_bar_0:     ; entry
        ; IMPLICIT_DEF
        lis r2, 15
        mullw r3, r3, r2
        blr

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16825 91177308-0d34-0410-b5e6-96231b3b80d8