MIPS32: ART Vectorizer

MIPS32 implementation which uses MSA extension.

Note: Testing is done with checker parts of tests 640, 645, 646 and
      651, locally changed to cover MIPS32 cases. These changes can't
      be included in this patch since MSA is not a default option.

Test: ./testrunner.py --target --optimizing -j1 in QEMU (mips32r6)
Change-Id: Ieba28f94c48c943d5444017bede9a5d409149762