doc: announce change in crypto adapter metadata

doc: announce change in crypto adapter metadata

In crypto adapter metadata, first 8 bytes of request info is a space
holder for response info. For better clarity, reserved field should be
removed from request info. New space for response info can be made by
changing type of event crypto metadata to structure from union.

Signed-off-by: Shijith Thotton <sthotton@marvell.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>
Acked-by: Ray Kinsella <mdr@ashroe.eu>
Acked-by: Jerin Jacob <jerinj@marvell.com>