NEON use vmov.i32 to splat some f32 values into vectors.

For bit patterns that aren't representable using the 8-bit floating point
representation for vmov.f32, but are representable via vmov.i32, treat
the .f32 syntax as an alias. Most importantly, this covers the case
'vmov.f32 Vd, #0.0'.

rdar://10616677

llvm-svn: 148556