S/390: Support z14 as CPU name.
    
    With IBM z14 officially announced I can add z14 as CPU name.
    
    No regressions with that patch on s390x.
    
    gas/ChangeLog:
    
    2017-07-26  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
    
    	Backport from mainline
    	2017-07-21  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
    
    	* config/tc-s390.c (s390_parse_cpu): Add z14 as alternate CPU
    	name.
    	* doc/as.texinfo: Add z14 to CPU string list.
    	* doc/c-s390.texi: Likewise.
    
    opcodes/ChangeLog:
    
    2017-07-26  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
    
    	Backport from mainline
    	2017-07-21  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
    
    	* s390-mkopc.c (main): Enable z14 as CPU string in the opcode
    	table.