s390: Be more verbose about missing operand type

s390: Be more verbose about missing operand type

Provide expected operand type in s390-specific assembler operand parsing
error message:

"error: operand <operand-number>: missing <operand-type> operand"

With <operand-type> being one of:
- base register
- displacement
- [vector] index register
- length
- access register
- control register
- floating-point register
- general-purpose register
- vector register
- [un]signed number

gas/
	* config/tc-s390.c: Provide missing operand type in error
	message.
	* testsuite/gas/s390/zarch-base-index-0-err.l: Update test case
	result validation patterns to operand number in operand syntax
	error messages.
	* testsuite/gas/s390/zarch-omitted-base-index-err.l: Likewise.

Reviewed-by: Andreas Krebbel <krebbel@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>