[X86] Remove some intel syntax aliases on (v)cvtpd2(u)dq, (v)cvtpd2ps,...

[X86] Remove some intel syntax aliases on (v)cvtpd2(u)dq, (v)cvtpd2ps, (v)cvt(u)qq2ps. Add 'x' and'y' suffix aliases to masked version of the same in att syntax.

The 128/256 bit version of these instructions require an 'x' or 'y' suffix to
disambiguate the memory form in att syntax.

We were allowing the same suffix in intel syntax, but it appears gas does not
do that.

gas does allow the 'x' and 'y' suffix on register and broadcast forms even
though its not needed. We were allowing it on unmasked register form, but not on
masked versions or on masked or unmasked broadcast form.

While there fix some test coverage holes so they can be extended with the 'x'
and 'y' suffix tests.

llvm-svn: 359418