Make some range based loop types more explicit.

No functional change, but more readable code.
ARM: cortex-m0 doesn't support unaligned memory access.

Unlike other v6+ processors, cortex-m0 never supports unaligned accesses.
From the v6m ARM ARM:

"A3.2 Alignment support: ARMv6-M always generates a fault when an unaligned
access occurs."

rdar://16491560
Simplify resolveFrameIndex() signature.

Just pass a MachineInstr reference rather than an MBB iterator.
Creating a MachineInstr& is the first thing every implementation did
anyway.