MIPS: TLAB allocation entrypoints

Add fast paths for TLAB allocation entrypoints for MIPS32 and MIPS64.
Also improve rosalloc entrypoints.

Note: All tests are executed on CI20 (MIPS32R2) and in QEMU (MIPS32R6
      and MIPS64R6), with and without ART_TEST_DEBUG_GC=true.

Test: ./testrunner.py --optimizing --target
Test: mma test-art-target-gtest
Test: mma test-art-host-gtest

Change-Id: I92195d2d318b26a19afc5ac46a1844b13b2d5191