- Reorg Thumb load / store instructions. Combine each rr and ri pair of

  instructions into one (e.g. tLDRrr, tLDRri -> tLDR).
- Thumb ldrsb and ldrsh only have the [reg, reg] address format. If the
  address is not an add, materialize a 0 immediate into a register and use
  it as the offset field.

llvm-svn: 33470