LoongArch: Redefine pattern for xvfrecip/vfrecip instructions.

LoongArch: Redefine pattern for xvfrecip/vfrecip instructions.

Redefine pattern for [x]vfrecip instructions use rtx code instead of unspec, and enable
[x]vfrecip instructions to be generated during auto-vectorization.

gcc/ChangeLog:

	* config/loongarch/lasx.md (lasx_xvfrecip_<flasxfmt>): Renamed to ..
	(recip<mode>3): .. this.
	* config/loongarch/loongarch-builtins.cc (CODE_FOR_lsx_vfrecip_d): Redefine
	to new pattern name.
	(CODE_FOR_lsx_vfrecip_s): Ditto.
	(CODE_FOR_lasx_xvfrecip_d): Ditto.
	(CODE_FOR_lasx_xvfrecip_s): Ditto.
	(loongarch_expand_builtin_direct): For the vector recip instructions, construct a
	temporary parameter const1_vector.
	* config/loongarch/lsx.md (lsx_vfrecip_<flsxfmt>): Renamed to ..
	(recip<mode>3): .. this.
	* config/loongarch/predicates.md (const_vector_1_operand): New predicate.