MIPS64: Fix LCodeGen::DoLoad/StoreKeyedExternalArray.
MIPS64: Fix some error in KeyedLoadIC.
MIPS64: Fix some small errors.
MIPS64: Fix various code-patching sequnces to use the updated li().

This includes:
     Assembler::RelocateInternalReference()
     RelocInfo::IsPatchedReturnSequence()
     BreakLocationIterator::SetDebugBreakAtReturn()
     BreakLocationIterator::SetDebugBreakAtSlot()
     FullCodeGenerator::EmitReturnSequence()
     Assembler::CheckTrampolinePool()

This is speculative fix, as much of this is not testable yet.
MIPS64: Fix a small error.
Merge remote-tracking branch 'origin/pl-mips64' into yy-dev-mips64
MIPS64: Fix some bugs in lithium-codegen.
MIPS64: Fix some bugs in macro-assembler.
MIPS64: Fix some bugs in stub-cache.
MIPS64: Fix some bugs in code-stubs.
MIPS64: Workaround the Smi::FromInt() bug for now, until we find a fix.
(cherry picked from commit e90b23c77ce129bda4254a09be215f7cf02430cd)
MIPS64: Fix wrong use is_int16/is_uint16.
Revert "MIPS64: Workaround the Smi::FromInt() bug for now, until we find a fix."

No longer needed after '42f8a367, MIPS64: Fix wrong use is_int16/is_uint16.'
which fixes the problem correctly.

This reverts commit c8dd12a970ebadd8727b166923063a6fc024961a.