[ARM] Use table-gen'd assembly operand diags in ARM asm parser

This switches the ARM AsmParser to use assembly operand diagnostics from
tablegen, rather than a switch statement on the ARMMatchResultTy. It
moves the existing diagnostic strings to tablegen, but adds no new ones,
so this is NFC except for one diagnostic string that had an off-by-1 error
in the hand-written switch statement.

Differential revision: https://reviews.llvm.org/D31607

llvm-svn: 314804