S/390: arch12: Add vllezlf instruction.

S/390: arch12: Add vllezlf instruction.

This adds support for the vector load element and zero instruction and
makes sure it is used when initializing vectors with elements while
setting the rest to 0.

gcc/ChangeLog:

2017-03-24  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* config/s390/s390.c (s390_expand_vec_init): Use vllezl
	instruction if possible.
	* config/s390/vector.md (vec_halfnumelts): New mode
	attribute.
	("*vec_vllezlf<mode>"): New pattern.

gcc/testsuite/ChangeLog:

2017-03-24  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* gcc.target/s390/vxe/vllezlf-1.c: New test.

From-SVN: r246455