aarch64: Reimplement vabdl_* intrinsics using builtins

aarch64: Reimplement vabdl_* intrinsics using builtins

Another simple set of intrinsic moved to builtins in the straightforward
way.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd-builtins.def (sabdl, uabdl):
	Define builtins.
	* config/aarch64/aarch64-simd.md (aarch64_<sur>abdl<mode>): New
	pattern.
	* config/aarch64/aarch64.md (unspec): Define UNSPEC_SABDL,
	UNSPEC_UABDL.
	* config/aarch64/arm_neon.h (vabdl_s8): Reimplemet using
	builtin.
	(vabdl_s16): Likewise.
	(vabdl_s32): Likewise.
	(vabdl_u8): Likewise.
	(vabdl_u16): Likewise.
	(vabdl_u32): Likewise.
	* config/aarch64/iterators.md (ABDL): New int iterator.
	(sur): Handle UNSPEC_SABDL, UNSPEC_UABDL.