MIPS64: Fix addu/subu overflow.

DoAddI's paramter is 64-bit(SMI) or 32-bit(constant).

mjsunit/regress/regress-int32-truncation
MIPS64: Use correct instruction.
MIPS64: Double data only use low 32-bit of one register.

TEST: mjsunit/compiler/minus-zero
MIPS64: Fix DoMulI when right is a negative constant(32-bit) and left is zero.

TEST: mjsunit/mul-exhaustive-part2 -- mjsunit/mul-exhaustive-part8
MIPS64: Fix 32-bit mul.

TEST: mjsunit/mul-exhaustive-part9
MIPS64: Fix the location for output of regexp.

Test: like mjsunit/regress/regress-latin-1, almost all regexp relative tests except
test/mjsunit/regexp.js.
MIPS64: Representation fix in DoStoreNamedField() and other two small fix.

Test: mjsunit/debug-liveedit-1 and many others.