s390: Treat addressing operand sequence as one in disassembler

s390: Treat addressing operand sequence as one in disassembler

Reuse logic introduced with the preceding commit in the assembler to
treat addressing operand sequences D(X,B), D(B), and D(L,B) as one
with regards to optional last operands (i.e. optparm and optparm2).

With this "nop" now disassembles into "nop" instead of "nop 0".

opcodes/
	* s390-dis.c (operand_count): New helper to count the remaining
	operands, treating D(X,B), D(B), and D(L,B) as one.
	(skip_optargs_p): New helper to test whether remaining operands
	 are optional.
	(skip_optargs_zero_p): New helper to test whether remaining
	operands are optional and their values are zero.
	(s390_print_insn_with_opcode): Use skip_optargs_zero_p to skip
	optional last operands with a value of zero.

gas/testsuite/
	* gas/s390/zarch-optargs.d (nop): Adjust test case accordingly.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>