IBM zSystems: Add support for z16 as CPU name.

So far z16 was identified as arch14. After the machine has been
announced we can now add the real name.

gas/ChangeLog:

	* config/tc-s390.c (s390_parse_cpu): Add z16 as alternate CPU
	name.
	* doc/as.texi: Add z16 and arch14 to CPU string list.
	* doc/c-s390.texi: Add z16 to CPU string list.

opcodes/ChangeLog:

	* s390-mkopc.c (main): Enable z16 as CPU string in the opcode
	table.