s390: Fix high-level builtins vec_gfmsum{,_accum}_128

s390: Fix high-level builtins vec_gfmsum{,_accum}_128

Starting with r14-9449-g9f2b16ce1efef0 builtins were streamlined with
those in LLVM.  In particular s390_vgfm{,a}g have been changed from
UV16QI to UINT128 in order to match those in LLVM.  However, these
low-level builtins are directly used by the high-level builtins
vec_gfmsum{,_accum}_128 which expect UV16QI instead.  Therefore,
introduce new low-level builtins s390_vgfm{,a}g_128 and make use of
them, respectively.

gcc/ChangeLog:

	* config/s390/s390-builtin-types.def (BT_FN_UV16QI_UV2DI_UV2DI):
	New.
	(BT_FN_UV16QI_UV2DI_UV2DI_UV16QI): New.
	* config/s390/s390-builtins.def (s390_vgfmg_128): New.
	(s390_vgfmag_128): New.
	* config/s390/vecintrin.h (vec_gfmsum_128): Use s390_vgfmg_128.
	(vec_gfmsum_accum_128): Use s390_vgfmag_128.