MIPS: Reduce size of LIR instruction by one word and remove dead code.

MIPS: Reduce size of LIR instruction by one word and remove dead code.

Port r11454 (72c662fc)

Original commit message:
Reduce size of LIR instruction by one word and remove dead code.

Until now we always recorded two deoptimization environments for instructions
that are marked as calls. We actually don't need two for all LIR
instructions except one (LInstanceOfKnownGlobal) where there is a lazy
deoptimization point in deferred code.

This change remove on of them and uses one virtual function instead
to make LInstanceOfKnownGlobal work as before.

Additionally, this change removes an unused predicate save_doubles_ from LIR
instructions and removes some helper functions that are used only in one place.

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=11501

[palfia, 2012-05-02 20:09:23]

Rebased on r11482

[danno, 2012-05-03 15:07:36]

LGTM. Landing.