aarch64: Reimplement vabd* intrinsics using builtins

aarch64: Reimplement vabd* intrinsics using builtins

This patch reimplements the vabd* intrinsics using RTL builtins.
It's fairly straightforward with new builtins + arm_neon.h changes.

gcc/
	* config/aarch64/aarch64-simd.md (aarch64_<su>abd<mode>_3):
	Rename to...
	(aarch64_<su>abd<mode>): ... This.
	(<sur>sadv16qi): Adjust callsite of the above.
	* config/aarch64/aarch64-simd-builtins.def (sabd, uabd): Define
	builtins.
	* config/aarch64/arm_neon.h (vabd_s8): Reimplement using
	builtin.
	(vabd_s16): Likewise.
	(vabd_s32): Likewise.
	(vabd_u8): Likewise.
	(vabd_u16): Likewise.
	(vabd_u32): Likewise.
	(vabdq_s8): Likewise.
	(vabdq_s16): Likewise.
	(vabdq_s32): Likewise.
	(vabdq_u8): Likewise.
	(vabdq_u16): Likewise.
	(vabdq_u32): Likewise.