MIPS: Change remaining entrypoints to save everything.

This also fixes two issues:
1. Missing restore of the callee-clobbered gp register on
   MIPS32
2. Incorrect DCHECK causing test 916-obsolete-jit to fail
   on MIPS32 in the ART_READ_BARRIER_TYPE=TABLELOOKUP
   configuration

Test: booted MIPS32R2 in QEMU
Test: test-art-target-gtest
Test: testrunner.py --target --optimizing
Test: booted MIPS64 (with 2nd arch MIPS32R2) in QEMU
Test: same tests as above for both MIPS32R6 and MIPS64R6
Test: repeat all of the above in two configurations:
      ART_READ_BARRIER_TYPE=TABLELOOKUP,
      ART_USE_READ_BARRIER=false.

Change-Id: I06a3c24579242a632ec8c373c233217d558a8401
7 files changed