ARM: fix WoA PEI instruction selection

The ARM::BLX instruction is an ARM mode instruction.  The Windows on ARM target
is limited to Thumb instructions.  Correctly use the thumb mode tBLXr
instruction.  This would manifest as an errant write into the object file as the
instruction is 4-bytes in length rather than 2.  The result would be a corrupted
object file that would eventually result in an executable that would crash at
runtime.
ARM: mark additional instructions as MachineFrameSetup

Mark up additional instructions which are part of the function prologue as
MachineFrameSetup.  These instructions are part of the function prologue,
emitted by the PEI pass to setup the stack for use in the activating frame.