x86emul: support of AVX512_IFMA insns

x86emul: support of AVX512_IFMA insns

Once again take the liberty and also correct the (public interface) name
of the AVX512_IFMA feature flag to match the SDM, on the assumption that
no external consumer has actually been using that flag so far.

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>