doc: announce eventdev ABI change to support DLB PMD

doc: announce eventdev ABI change to support DLB PMD

The ABI changes associated with this notification will better support
devices that:
1. Have limits on the number or queues that may be linked to a port
2. Have ports that are limited to exactly one linked queue
3. Are not able to transparently transfer the event flow_id field

Signed-off-by: Timothy McDaniel <timothy.mcdaniel@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>