octeontx2-af: Relax resource lock into mutex

Mailbox message handling is done in a workqueue context scheduled
from interrupt handler. So resource locks does not need to be a spinlock.
Therefore relax them into a mutex so that later on we may use them
in routines that might sleep.

Signed-off-by: Stanislaw Kardach <skardach@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>