Rename the glibc.tune namespace to glibc.cpu

The glibc.tune namespace is vaguely named since it is a 'tunable', so
give it a more specific name that describes what it refers to.  Rename
the tunable namespace to 'cpu' to more accurately reflect what it
encompasses.  Also rename glibc.tune.cpu to glibc.cpu.name since
glibc.cpu.cpu is weird.

	* NEWS: Mention the change.
	* elf/dl-tunables.list: Rename tune namespace to cpu.
	* sysdeps/powerpc/dl-tunables.list: Likewise.
	* sysdeps/x86/dl-tunables.list: Likewise.
	* sysdeps/aarch64/dl-tunables.list: Rename tune.cpu to
	cpu.name.
	* elf/dl-hwcaps.c (_dl_important_hwcaps): Adjust.
	* elf/dl-hwcaps.h (GET_HWCAP_MASK): Likewise.
	* manual/README.tunables: Likewise.
	* manual/tunables.texi: Likewise.
	* sysdeps/powerpc/cpu-features.c: Likewise.
	* sysdeps/unix/sysv/linux/aarch64/cpu-features.c
	(init_cpu_features): Likewise.
	* sysdeps/x86/cpu-features.c: Likewise.
	* sysdeps/x86/cpu-features.h: Likewise.
	* sysdeps/x86/cpu-tunables.c: Likewise.
	* sysdeps/x86_64/Makefile: Likewise.
	* sysdeps/x86/dl-cet.c: Likewise.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>