MIPS: Consistently use a separate Lithium instruction for flooring division.

MIPS: Consistently use a separate Lithium instruction for flooring division.

Port r20395 (5b802048)

Original commit message:
Previously we tried to share some code on by a slightly confusing re-use
of LDivI for a (general) flooring division. Now we cleanly separate
concerns, just like for the rest of the division-like operations. Note
that ARM64 already did it this way.

If we really want to save some code, we can introduce some macro
assembler instructions and/or helper functions in the code generator in
a future CL, but we should really try to avoid being "clever" to save
just a few lines of trivial code. Effort != complexity. :-)

Renamed some related Lithium operands on the way for more consistency.

BUG=
R=plind44@gmail.com

Committed: https://code.google.com/p/v8/source/detail?r=20417

[palfia, 2014-04-01 22:53:32]

PTAL.

[Paul Lind, 2014-04-01 23:37:39]

LGTM.

[palfia, 2014-04-01 23:43:56]

Committed patchset #1 manually as r20417 (presubmit successful).