s390: Extend two/four element integer vectors

s390: Extend two/four element integer vectors

For the moment I deliberately left out one-element QHS vectors since it
is unclear whether these are pathological cases or whether they are
really used.  If we ever get an extend for V1DI -> V1TI we should
reconsider this.

As a side-effect this fixes PR115261.

gcc/ChangeLog:

	PR target/115261
	* config/s390/s390.md (any_extend,extend_insn,zero_extend):
	New code attributes and code iterator.
	* config/s390/vector.md (V_EXTEND): New mode iterator.
	(<extend_insn><V_EXTEND:mode><vec_2x_wide>2): New insn.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/vector/vec-extend-1.c: New test.
	* gcc.target/s390/vector/vec-extend-2.c: New test.