ticketlock: promote as stable

ticketlock: promote as stable

As rte_ticketlock was introduced in 19.05 release
and there were no changes in its public API since
19.11 release, it should be mature enough to remove
the experimental tag.

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: David Christensen <drc@linux.vnet.ibm.com>