MIPS: Improve InstructionCodeGeneratorMIPS*::GenerateSuspendCheck().

Relax the only back-edge restriction. Implement optimization for
MIPS32/MIPS64 which has already been done for the ARM & x86
architectures in
https://android-review.googlesource.com/#/c/platform/art/+/149370/.

Test: Boot & run tests on 32- & 64-bit version of QEMU.
Test: test/testrunner/testrunner.py --target --optimizing
Test: test-art-host-gtest
Test: test-art-target-gtest

Change-Id: Ie0a4c19ee50ad532fe53933d5808f9d7a4f89b8e