s390: Deprecate some vector builtins

According to IBM Open XL C/C++ for z/OS version 1.1 builtins

- vec_permi
- vec_ctd
- vec_ctsl
- vec_ctul
- vec_ld2f
- vec_st2f

are deprecated.  Also deprecate helper builtins vec_ctd_s64 and
vec_ctd_u64.

Furthermore, the overloads of vec_insert which make use of a bool vector
are deprecated, too.

gcc/ChangeLog:

	* config/s390/s390-builtins.def (vec_permi): Deprecate.
	(vec_ctd): Deprecate.
	(vec_ctd_s64): Deprecate.
	(vec_ctd_u64): Deprecate.
	(vec_ctsl): Deprecate.
	(vec_ctul): Deprecate.
	(vec_ld2f): Deprecate.
	(vec_st2f): Deprecate.
	(vec_insert): Deprecate overloads with bool vectors.