S/390: z13: Accept vector alignment hints

Accept vector alignment hints on z13 although they are ignored there.
The advantage is that any binary compiled for architecture level z13 may
run on z14 or later and benefit from vector alignment hints.

Backport from mainline.

gas/ChangeLog:

2020-05-18  Stefan Schulze Frielinghaus  <stefansf@linux.ibm.com>

	* testsuite/gas/s390/zarch-z13.d: Add regexp checks for vector
	load/store instruction variants with alignment hints.
	* testsuite/gas/s390/zarch-z13.s: Emit new vector load/store
	instruction variants with alignment hints.

opcodes/ChangeLog:

2020-05-18  Stefan Schulze Frielinghaus  <stefansf@linux.ibm.com>

	* s390-opc.txt: Relocate vector load/store instructions with
	additional alignment parameter and change architecture level
	constraint from z14 to z13.