aarch64: Merge sqdmlal2 and sqdmlsl2 expanders

The various sqdmlal2 and sqdmlsl2 expanders perform almost identical functions and can be
merged using code iterators and attributes to reduce the code in the MD file.
No behavioural change is expected.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd.md (aarch64_sqdmlal2<mode>): Merge into...
	(aarch64_sqdml<SBINQOPS:as>l2<mode>): ... This.
	(aarch64_sqdmlsl2<mode>): Delete.
	(aarch64_sqdmlal2_lane<mode>): Merge this...
	(aarch64_sqdmlsl2_lane<mode>): ... And this...
	(aarch64_sqdml<SBINQOPS:as>l2_lane<mode>): ... Into this.
	(aarch64_sqdmlal2_laneq<mode>): Merge this...
	(aarch64_sqdmlsl2_laneq<mode>): ... And this...
	(aarch64_sqdml<SBINQOPS:as>l2_laneq<mode>): ... Into this.
	(aarch64_sqdmlal2_n<mode>): Merge this...
	(aarch64_sqdmlsl2_n<mode>): ... And this...
	(aarch64_sqdml<SBINQOPS:as>l2_n<mode>): ... Into this.