net: thunderx: make CFG_DONE message to run through generic send-ack sequence

At the end of NIC VF initialization VF sends CFG_DONE message to PF without
using nicvf_msg_send_to_pf routine. This potentially could re-write data in
mailbox. This commit is to implement common way of sending CFG_DONE message
by the same way with other configuration messages by using
nicvf_send_msg_to_pf() routine.

Signed-off-by: Vadim Lomovtsev <vlomovtsev@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>