ARM: Add a few missing add->sub aliases w/ 'w' suffix.

Aliases for adding a negative immediate when using an explicit 'w'
suffix. E.g.,
        adds.w r2, #-16
        adds.w r2, r2, #-16
        addw r2, #-16
        addw r2, #-16
        addw r2, r2, #-16

rdar://11330769

llvm-svn: 155946