examples/ipsec-secgw: support internal ports for events

examples/ipsec-secgw: support internal ports for events

Add support for Rx and Tx internal ports. When internal ports are
available then a packet can be received from eth port and forwarded
to event queue by HW without any software intervention. The same
applies to Tx side where a packet sent to an event queue can by
forwarded by HW to eth port without any software intervention.

Signed-off-by: Anoob Joseph <anoobj@marvell.com>
Signed-off-by: Lukasz Bartosik <lbartosik@marvell.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>