AArch64: correct dot-product RTL patterns for aarch64.

AArch64: correct dot-product RTL patterns for aarch64.

The previous fix for this problem was wrong due to a subtle difference between
where NEON expects the RMW values and where intrinsics expects them.

The insn pattern is modeled after the intrinsics and so needs an expand for
the vectorizer optab to switch the RTL.

However operand[3] is not expected to be written to so the current pattern is
bogus.

Instead I rewrite the RTL to be in canonical ordering and merge them.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd-builtins.def (sdot, udot): Rename to..
	(sdot_prod, udot_prod): ... This.
	* config/aarch64/aarch64-simd.md (aarch64_<sur>dot<vsi2qi>): Merged
	into...
	(<sur>dot_prod<vsi2qi>): ... this.
	(aarch64_<sur>dot_lane<vsi2qi>, aarch64_<sur>dot_laneq<vsi2qi>):
	Change operands order.
	(<sur>sadv16qi): Use new operands order.
	* config/aarch64/arm_neon.h (vdot_u32, vdotq_u32, vdot_s32,
	vdotq_s32): Use new RTL ordering.