s390: Provide operand number in assembler warning and error messages

s390: Provide operand number in assembler warning and error messages

Prepend the operand number "operand %d:" to the s390-specific assembler
operand parsing warning and error messages.

While at it reword the custom operand out of range error message text to
be closer to the one used by as_bad_value_out_of_range(). Additionally
reword the invalid FPR pair warning message to make it nicer.

gas/
	* config/tc-s390.c: Print operand number in error messages.
	* testsuite/gas/s390/zarch-base-index-0-err.l: Update test case
	verification patterns to accept syntax error messages now
	containing the operand number.
	* testsuite/gas/s390/zarch-omitted-base-index-err.l: Likewise.
	* testsuite/gas/s390/zarch-warn-areg-zero.l: Likewise.
	* testsuite/gas/s390/zarch-z9-109-err.l: Likewise.
	* testsuite/gas/s390/zarch-z900-err.l: Likewise.

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