aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK

Now that LD_HWCAP_MASK (or glibc.tune.hwcap_mask) is read early enough
to influence cpu feature check in aarch64, use it to influence
multiarch selection.  Setting LD_HWCAP_MASK such that it clears
HWCAP_CPUID will now disable multiarch for the binary.

HWCAP_CPUID is also now set in HWCAP_IMPORTANT so that it is set by
default.  With this patch, this feature is only usable with
dyanmically linked binaries because LD_HWCAP_MASK is not read for
static binaries.  A future patch fixes that.

	* sysdeps/unix/sysv/linux/aarch64/cpu-features.c
	(init_cpu_features): Use glibc.tune.hwcap_mask.
	* sysdeps/unix/sysv/linux/aarch64/dl-procinfo.h: New file.