s390: arch15: Vector load positive: Add 128-bit integer support

For previous architectures emulate operation abs.

gcc/ChangeLog:

	* config/s390/s390-builtins.def (s390_vec_abs_s128): Add.
	(s390_vlpq): Add.
	* config/s390/s390-builtin-types.def: Update accordingly.
	* config/s390/vector.md (abs<mode>2): Emulate w/o VXE3.
	(*abs<mode>2): Add 128-bit variant.
	(*vec_sel0<mode>): Make it a ...
	(vec_sel0<mode>): named pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/vector/vec-abs-emu.c: New test.