examples/ipsec-secgw: add event helper config init/uninit

Add eventmode helper eh_conf_init and eh_conf_uninit
functions which purpose is to initialize and
uninitialize eventmode helper configuration.

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>