ARM: Thumb2 LDR(literal) can target SP.

Fix a slightly overzealous destination register restriction for the
'without .w' alias. Add some explicit testcases.

rdar://16033140

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201173 91177308-0d34-0410-b5e6-96231b3b80d8
Tidy up a bit. Formatting only.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@201174 91177308-0d34-0410-b5e6-96231b3b80d8