x86: adjust/correct VFRCZ{P,S}{S,D} decoding

The unnecessary XOP.L decoding had caught my eye, together with the not
really expected operand specifiers. Drop this decode step, and instead
make sure XOP.W and XOP.PP don't get ignored. For the latter, do this in
a form applicable to all XOP insns, rather than adding extra table
layers - there are no encodings with the field non-zero. Besides these
two, for the scalar forms XOP.L actually needs to also be zero.