Hi,
This patch builds on Mihai Popa's steps towards supporting the edge cases of ARM's "modified immediate" format instructions. That patch should probably be committed first.
The instructions he added were actually much closer to the ideal MC representation of what's going on than the existing set, but it was decided that removing the originals in one massive patch would be too invasive, so this is a step in that direction.
It converts the instructions he added into the canonical assembly representation for these operations (with some slightly annoying accommodations for TableGen). The next step will be converting CodeGen to use these versions and eventually removing the legacy representation entirely.