[X86] Merge the FR128 and VR128 regclass since they have identical spill and alignmen...

[X86] Merge the FR128 and VR128 regclass since they have identical spill and alignment characteristics.

This unfortunately requires a bunch of bitcasts to be added added to SUBREG_TO_REG, COPY_TO_REGCLASS, and instructions in output patterns. Otherwise tablegen seems to default to picking f128 and then we fail when something tries to get the register class for f128 which isn't always valid.

The test changes are because we were previously mixing fr128 and vr128 due to contrainRegClass finding FR128 first and passes like live range shrinking weren't handling that well.

llvm-svn: 337147