Created by: fhahn
This commit adds encoder/decoder support for fmov from GPRs to FPRs.
It does not add support for the variant to move a 64 bit GPR to the top
of a 128 bit register (FMOV <Vd>.D[1], <Xn>). I think for that variant,
we would need a way to express the top half of a 128 bit register.
Issue #2626