S/390: Support vector alignment hints

S/390: Support vector alignment hints

This patch adds the vector alignment hints to the vector load and
store instructions as documented in the IBM z14 Principles of
Operations manual:

http://publibfi.boulder.ibm.com/epubs/pdf/dz9zr011.pdf

opcodes/ChangeLog:

2018-10-23  Andreas Krebbel  <krebbel@linux.ibm.com>

	* s390-opc.txt: Add vector load/store instructions with additional
	alignment parameter.

gas/ChangeLog:

2018-10-23  Andreas Krebbel  <krebbel@linux.ibm.com>

	* config/tc-s390.c (md_gather_operands): Fix for optional operands
	following memory addresses.
	* testsuite/gas/s390/zarch-arch12.d: Add regexp checks for new
	instruction variants.
	* testsuite/gas/s390/zarch-arch12.s: Emit new instruction
	variants.