eventdev: improve error handling for Rx adapter queue add/del

eventdev: improve error handling for Rx adapter queue add/del

The new WRR sequence applicable after queue add/del is set
up after setting the new queue state, so a memory allocation
failure will leave behind an incorrect state.

This change separates the memory sizing + allocation for the
Rx poll and WRR array from calculation of the WRR sequence.
If there is a memory allocation failure, existing Rx queue
configuration remains unchanged.

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>