s390: Optionally print instruction description in disassembly

Print instruction description as comment in disassembly with s390
architecture specific option "insndesc":

- For objdump it can be enabled with option "-M insndesc"
- In gdb it can be enabled with "set disassembler-options insndesc"

Since comments are not column aligned the output can enhanced for
readability by postprocessing using a filter such as "expand":

... | expand -t 8,16,24,32,40,80

Or when using in combination with objdump option --visualize-jumps:

... | expand | sed -e 's/ *#/\t#/' | expand -t 1,80

Note that the instruction descriptions add about 128 KB to s390-opc.o:

s390-opc.o without instruction descriptions: 216368 bytes
s390-opc.o with instruction descriptions   : 348432 bytes

binutils/
	* NEWS: Mention new s390-specific disassembler option
	  "insndesc".

include/
	* opcode/s390.h (struct s390_opcode): Add field to hold
	  instruction description.

opcodes/
	* s390-mkopc.c: Copy instruction description from s390-opc.txt
	  into generated operation code table s390-opc.tab.
	* s390-opc.c (s390_opformats): Provide NULL as description in
	  .insn pseudo-mnemonics opcode table.
	* s390-dis.c: Add s390-specific disassembler option "insndesc"
	  and optionally print the instruction description as comment in
	  the disassembly when it is specified.

gas/
	* testsuite/gas/s390/s390.exp: Add new test disassembly test
	  case "zarch-insndesc".
	* testsuite/gas/s390/zarch-insndesc.s: New test case for s390-
	  specific disassembler option "insndesc".
	* testsuite/gas/s390/zarch-insndesc.d: Likewise.

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

include/opcode/s390.h

@@ -81,7 +81,7 @@ enum s390_opcode_cpu_val
 
 struct s390_opcode
   {
-    /* The opcode name.  */
+    /* The opcode name (mnemonic).  */
     const char * name;
 
     /* The opcode itself.  Those bits which will be filled in with
@@ -110,6 +110,9 @@ struct s390_opcode
 
     /* Instruction specific flags.  */
     unsigned int flags;
+
+    /* Instruction description.  */
+    const char * description;
   };
 
 /* The table itself is sorted by major opcode number, and is otherwise