arm64: use shared sysctl constants

Use shared sysctl variables for zero and one constants, as in
commit eec4844f ("proc/sysctl: add shared variables for range check")

Fixes: 63f0c603 ("arm64: Introduce prctl() options to control the tagged user addresses ABI")
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: Will Deacon <will@kernel.org>