net: thunderx: mailboxes: remove code duplication

Use the nicvf_send_msg_to_pf() function in the mailbox code.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>