[AVX-512] Remove masked pmovzx/pmovsx builtins and autoupgrade them to selects...

[AVX-512] Remove masked pmovzx/pmovsx builtins and autoupgrade them to selects and native zext/sext.

This mostly reuses earlier autoupgrade support for the sse and avx equivalents. Just needed to add the code to add the select.

llvm-svn: 286092