eventdev: reserve space in main structs for extension
eventdev: reserve space in main structs for extension

The struct rte_eventdev and rte_eventdev_data are supposed
to be used internally only, but there is a chance that
increasing their size would break ABI for some applications.
In order to allow smooth addition of features without breaking
ABI compatibility, some space is reserved.

Signed-off-by: Jerin Jacob <352c4d4f9291b869992ddb67daa45ddc149fed30@marvell.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk