x86: reduce amount of various VCVT* templates

x86: reduce amount of various VCVT* templates

Presumably as a result of various changes over the last several months,
and - for some of them - with a generalization of logic in
match_mem_size() plus mirroring of this generalization into the
broadcast handling logic of check_VecOperands(), various register-only
templates can be foled into their respective memory forms. This in
particular then also allows dropping a few more instances of IgnoreSize.