Clean up ARM fused multiply + add/sub support some more: rename some isel

predicates.
Also remove NEON2 since it's not really useful and it is confusing. If
NEON + VFP4 implies NEON2 but NEON2 doesn't imply NEON + VFP4, what does it
really mean?

rdar://10139676

llvm-svn: 154480