x86emul: support AVX512_VNNI insns

x86emul: support AVX512_VNNI insns

Along the lines of the 4FMAPS case, convert the 4VNNIW-based table
entries to a decoder adjustment. Because of the current sharing of table
entries between different (implied) opcode prefixes and with the same
major opcodes being used for vp4dpwssd{,s}, which have a different
memory operand size and different Disp8 scaling, the pre-existing table
entries get converted to a decoder override. The table entries will now
represent the insns here, in line with other table entries preferably
representing the prefix-66 insns.

As in a few cases before, since the insns here and in particular their
memory access patterns follow the usual scheme, I didn't think it was
necessary to add a contrived test specifically for them, beyond the
Disp8 scaling one.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>