MIPS: Improvements in lithium code generation. Recognizing if some operands are constants, we can often save on registers and instructions.

Port r14364 (2819e5ee)

BUG=

Review URL: https://codereview.chromium.org/14159015

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14383 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: ARM: Fix erroneous detection of Double result type in Integer32 BinaryOpStubs

Port r14371 (b5c4a990)

BUG=

Review URL: https://codereview.chromium.org/13973013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14384 ce2b1a6d-e550-0410-aec6-3dcde31c8c00