S/390: Remove trailing zeros on 4-bytes opcodes.

S/390: Remove trailing zeros on 4-bytes opcodes.

This is a NOP change only relevant when reading the file or parsing it
with other tools.

opcodes/ChangeLog:

2015-09-09  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* s390-opc.c: Add OP32 definition.
	* s390-opc.txt: Reduce the opcode padding of some extended
	mnemonics from 6 to the actual length (which is 4).