MIPS32: Change java.lang.Math.abs(float/double) intrinsics

abs.s and abs.d instructions can't be used when NAN2008=0 (R2 and
before). In these cases, abs(NaN) might change other bits (not just
sign bit).

This fixes test failure 631-checker-fp-abs for MIPS32.

Bug: 30758343
Test: mma test-art-target-run-test on CI20

Change-Id: I352efd66f2f72740406462c9ccc3bc4b1b5aea20