MIPS: Drop unnecessary receiver validity checks from {Load,Store}IC_Normal.

Port r22391 (fe86010)

Original commit message:
Since these builtins are used as handlers after a map check/dispatch, they don't need to check the receiver again.

BUG=
R=akos.palfi@imgtec.com

Review URL: https://codereview.chromium.org/396663004

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22411 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Fix r19500 register usage to match to ASSERT.

BUG=
R=akos.palfi@imgtec.com

Review URL: https://codereview.chromium.org/395863002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22412 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
MIPS: Minor fixes to r22396

BUG=
R=akos.palfi@imgtec.com

Review URL: https://codereview.chromium.org/394913002

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22413 ce2b1a6d-e550-0410-aec6-3dcde31c8c00