IBM zSystems: Add support for z16 as CPU name.

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.

gcc/ChangeLog:

	* common/config/s390/s390-common.cc: Rename PF_ARCH14 to PF_Z16.
	* config.gcc: Add z16 as march/mtune switch.
	* config/s390/driver-native.cc (s390_host_detect_local_cpu):
	Recognize z16 with -march=native.
	* config/s390/s390-opts.h (enum processor_type): Rename
	PROCESSOR_ARCH14 to PROCESSOR_3931_Z16.
	* config/s390/s390.cc (PROCESSOR_ARCH14): Rename to ...
	(PROCESSOR_3931_Z16): ... throughout the file.
	(s390_processor processor_table): Add z16 as cpu string.
	* config/s390/s390.h (enum processor_flags): Rename PF_ARCH14 to
	PF_Z16.
	(TARGET_CPU_ARCH14): Rename to ...
	(TARGET_CPU_Z16): ... this.
	(TARGET_CPU_ARCH14_P): Rename to ...
	(TARGET_CPU_Z16_P): ... this.
	(TARGET_ARCH14): Rename to ...
	(TARGET_Z16): ... this.
	(TARGET_ARCH14_P): Rename to ...
	(TARGET_Z16_P): ... this.
	* config/s390/s390.md (cpu_facility): Rename arch14 to z16 and
	check TARGET_Z16 instead of TARGET_ARCH14.
	* config/s390/s390.opt: Add z16 to processor_type.
	* doc/invoke.texi: Document z16 and arch14.