doc: announce deprecation of dpaa2 exposed mem structure

doc: announce deprecation of dpaa2 exposed mem structure

rte_dpaa2_memsegs is no more required once the dpaax (pa-va) translation
library has been introduced. This can be made internal (for fallback
operations) in subsequent release.

Signed-off-by: Shreyansh Jain <shreyansh.jain@nxp.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Acked-by: Anatoly Burakov <anatoly.burakov@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>