MIPS32: Properly handle doubles in GetRegisterIfAccessible

There was a problem with floating point registers and exception
handler. In optimizing compiler fpu registers are treated as 64-bit.
This is problematic since logic in GetRegisterIfAccessible doesn't
support 64-bit floating point registers.

This fixes tests:
    510-checker-try-catch
    534-checker-bce-deoptimization

Test: mma test-art-target on CI20 (mips32r2) and emulator (mips32r6)

Change-Id: I0f49c1c30f97077b82ad08fcc3cdb86a4877af23