PowerPC inline asm was emitting two output operands

PowerPC inline asm was emitting two output operands
for a single "m" constraint; this is wrong because the
opcode of a load or store would have to change in parallel.
This patch makes it always compute addresses into a register,
which is correct but not as efficient as possible.  7144566.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79292 91177308-0d34-0410-b5e6-96231b3b80d8