ring: use WFE to wait for tail update on aarch64

ring: use WFE to wait for tail update on aarch64

Instead of polling for tail to be updated, use WFE instruction.

Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>