x86: Use explicit shift count in double-precision shifts

Don't use implicit shift count in double-precision shifts in AT&T syntax
since they aren't in Intel SDM.  Keep the 's' modifier for backward
compatibility with inline asm statements.

	PR target/114590
	* config/i386/i386.md (x86_64_shld): Use explicit shift count in
	AT&T syntax.
	(x86_64_shld_ndd): Likewise.
	(x86_shld): Likewise.
	(x86_shld_ndd): Likewise.
	(x86_64_shrd): Likewise.
	(x86_64_shrd_ndd): Likewise.
	(x86_shrd): Likewise.
	(x86_shrd_ndd): Likewise.