ARM/ARM64: Extend support of instruction combining.

Combine multiply instructions in the following way:
ARM64:
MUL/NEG -> MNEG
ARM32 (32-bit integers only):
MUL/ADD -> MLA
MUL/SUB -> MLS

Change-Id: If20f2d8fb060145ab6fbceeb5a8f1a3d02e0ecdb
17 files changed