cryptodev: define value for unlimited sessions

cryptodev: define value for unlimited sessions

Currently, the info structure contains the maximum number
of sessions that a device can manage.
This field was useful when the session mempool was created inside
each device, but now it is created at the application level.

Most PMDs do not have a limitation on the sessions managed,
but a few do, therefore this field must remain in the structure.
However, a new value, 0, can be used to indicate that
a device does not have an actual maximum of sessions.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>