MIPS: Support kJitTableAddress kinds of string/class loads.

Also remove a few stale comments.

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

Change-Id: I8914b8e6594e030f8137e7fface1ae20b6d6b971