Add ARM .movsp unwind directive.

Patch by Ilyong Cho.
Add FrameSetup to MIFlag in ARMFrameLowering.
Add test cases.
Flush the pending offset before emitting the movsp directive.
Fix typo.
Reword the assertion.
Fix typo.
Revert "Add FrameSetup to MIFlag in ARMFrameLowering."

The .movsp might be emitted after the .setfp directive,
which will result in compilation error in some real-world
application.

This reverts commit bec12d6f6fcc8521db873aa9d749dde97f4bb36a.
Fix typo: The condition should be reverted.

The condition in the ARMAsmParser should be reverted so that
it can match the assertion in the codegen.
Initialize FPReg for .movsp properly.