eventdev/eth_rx: make enqueue buffer circular

eventdev/eth_rx: make enqueue buffer circular

Rx adapter uses memove() to move unprocessed events to the beginning of
the packet enqueue buffer. The use memmove() was found to consume good
amount of CPU cycles (about 20%).

This patch removes the use of memove() while implementing a circular
buffer to avoid copying of data. With this change RX adapter is able
to fill the buffer of 16384 events.

Signed-off-by: Ganapati Kundapura <ganapati.kundapura@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>