MIPS64: ART Vectorizer

MIPS64 implementation which uses MSA extension. Also extended all
relevant checker tests to test MIPS64 implementation.

Test: booted MIPS64R6 in QEMU
Test: ./testrunner.py --target --optimizing -j1 in QEMU

Change-Id: I8b8a2f601076bca1925e21213db8ed1d41d79b52
23 files changed