MIPS32R2: Allow all kinds of class/string loads and invokes

Force generating nal instruction before PC-relative addressing in the
presence of irreducible loops (HMipsComputeBaseMethodAddress is not
used in those situations).

This patch fixes a lot of JIT tests failures.

Test: ./testrunner.py --target --optimizing --jit (CI20 and QEMU)
Test: mma test-art-target-gtest (CI20 and QEMU)

Change-Id: I1815a6bb5783f439c8263612abff557f797bfef1