event/cnxk: add option for in-flight buffer count

event/cnxk: add option for in-flight buffer count

The number of events for a *open system* event device is specified
as -1 as per the eventdev specification.
Since, SSO inflight events are only limited by DRAM size, the
xae_cnt devargs parameter is introduced to provide upper limit for
in-flight events.

Example:
        --dev "0002:0e:00.0,xae_cnt=8192"

Signed-off-by: Shijith Thotton <sthotton@marvell.com>
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>