Add support for vmov.f64/.f32 encoding. There's a bit of a hack going on

here. The f32 in FCONSTS is handled as a double instead of a float in the
code. So the encoding of the immediate into the instruction isn't exactly in
line with the documentation in that regard. But given that we know it's handled
as a double, it doesn't cause any harm.

llvm-svn: 116471