aarch64: Add hwcap string routines

Add support for routines in dl-procinfo.h to show string versions of
HWCAP entries when a program is invoked with the LD_SHOW_AUXV
environment variable set and also to aid in path resolution for
ldconfig.

	* sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c
	(_dl_aarch64_cap_flags): New array.
	* sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h
	(_dl_hwcap_string, _dl_string_hwcap, _dl_procinfo): Implement
	functions.