s390: arch15: Vector generate element masks

s390: arch15: Vector generate element masks

Add instruction vgem and vector builtins
vec_gen_element_masks_{8,16,32,64,128}.

gcc/ChangeLog:

	* config/s390/s390-builtins.def (s390_vec_gen_element_masks_128): Add.
	(s390_vgemb): Add.
	(s390_vgemh): Add.
	(s390_vgemf): Add.
	(s390_vgemg): Add.
	(s390_vgemq): Add.
	* config/s390/s390-builtin-types.def: Update accordingly.
	* config/s390/s390.md (UNSPEC_VEC_VGEM): Add.
	* config/s390/vecintrin.h (vec_gen_element_masks_8): Define.
	(vec_gen_element_masks_16): Define.
	(vec_gen_element_masks_32): Define.
	(vec_gen_element_masks_64): Define.
	(vec_gen_element_masks_128): Define.
	* config/s390/vx-builtins.md (vgemv16qi): Add.
	(vgem<mode>): Add.