x86/Intel: SHLD/SHRD have dual meaning

Since we uniformly permit D suffixes in Intel mode whenever in AT&T mode
an L suffix may be used, we need to be consistent with this.

Take the easy route, despite that still leading to an anomaly which is
also visible from the new testcase:

	shld	eax, ecx, 1
	shld	eax, ecx, cl

can mean two things with APX: SHL with a D suffix in NDD EVEX encoding,
or the traditional SHLD in legacy encoding.