MIPS32R6: Improve PC-relative string/class loads and invokes.

Use PC-relative addressing on MIPS32R6 instead of
HMipsDexCacheArraysBase and allow such PC-relative
addressing in presence of irreducible loops.

Also save a couple of instructions when handling
string and class loads from bss.

Test: test-art-host-gtest
Test: booted MIPS32R2 in QEMU
Test: "make -j1 ART_TEST_DEFAULT_COMPILER=false ART_TEST_OPTIMIZING=true
       ART_TEST_INTERPRETER=false ART_TEST_JIT=false
       ART_TEST_PIC_TEST=true test-art-target-run-test"
Test: booted MIPS64 (with 2nd arch MIPS32R6) in QEMU
Test: "make -j1 ART_TEST_DEFAULT_COMPILER=false ART_TEST_OPTIMIZING=true
       ART_TEST_INTERPRETER=false ART_TEST_JIT=false
       ART_TEST_PIC_TEST=true test-art-target-run-test32"

Change-Id: I5d0fcbf271541294a3d4479987d52e2aaff084d9
8 files changed