ARM: fix folding stack adjustment (again again again...)

This time, the issue is that we weren't accounting for the possibility that
aligned DPRs could have been stored after the final "push" in a prologue. When
that happened we effectively moved a "sub sp, #N" from below the aligned stores
to above them, and everything went to pot.

To make it worse, I'd actually committed something testing that we produced
wrong code, so the test update is tiny.

llvm-svn: 248437