RDMA/efa: Improve admin completion context state machine

RDMA/efa: Improve admin completion context state machine

Add a new unused state to the admin completion contexts state machine
instead of the occupied field. This improves the completion validity
check because it now enforce the context to be in submitted state prior
to completing it. Also add allocated state as a intermediate state
between unused and submitted.

Reviewed-by: Daniel Kranzdorf <dkkranzd@amazon.com>
Reviewed-by: Michael Margolin <mrgolin@amazon.com>
Signed-off-by: Yonatan Nachum <ynachum@amazon.com>
Link: https://patch.msgid.link/20251210130614.36460-3-ynachum@amazon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>