MIPS: Cleanup handling of shifts: SHR can deoptimize only when its a shift by 0, all other shift never deoptimize.

Port r12373 (9fdde2ad)

Original commit message:
Fix DoDeferredNumberTagU to keep the value in xmm1 instead of xmm0 on x64.

xmm0 is not saved across runtime call on x64 because MacroAssembler::EnterExitFrameEpilogue preserves only allocatable XMM registers unlike on ia32 where it preserves all registers.

Cleanup handling of shifts: SHR can deoptimize only when its a shift by 0, all other shift never deoptimize.

Fix type inference for i-to-t change instruction. On X64 this ensures that write-barrier is generated correctly.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10876054
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12831 ce2b1a6d-e550-0410-aec6-3dcde31c8c00