[2/4] aarch64: Convert UABDL2 and SABDL2 patterns to standard RTL codes

[2/4] aarch64: Convert UABDL2 and SABDL2 patterns to standard RTL codes

Similar to the previous patch for UABDL and SABDL, this patch covers the *2 versions that vec_select the high half
of its input to do the asbsdiff and extend. A define_expand is added for the intrinsic to create the "select-high-half" RTX the pattern expects.

Bootstrapped and tested on aarch64-none-linux-gnu.

gcc/ChangeLog:

	* config/aarch64/aarch64-simd.md (aarch64_<sur>abdl2<mode>): Rename to...
	(aarch64_<su>abdl2<mode>_insn): ... This.  Use RTL codes instead of unspec.
	(aarch64_<su>abdl2<mode>): New define_expand.
	* config/aarch64/aarch64.md (UNSPEC_SABDL2, UNSPEC_UABDL2): Delete.
	* config/aarch64/iterators.md (ABDL2): Delete.
	(sur): Remove handling of UNSPEC_SABDL2 and UNSPEC_UABDL2.