Enable VDSO for static linking on aarch64

	[BZ #19767]
	* sysdeps/unix/sysv/linux/aarch64/init-first.c: Remove #ifdef SHARED.
	* sysdeps/unix/sysv/linux/aarch64/libc-vdso.h: Remove #ifdef SHARED.
	* sysdeps/unix/sysv/linux/aarch64/sysdep.h (ALWAYS_USE_VSYSCALL):
	Define.