net: microchip: sparx5: Add VCAP admin locking in debugFS

This ensures that the admin lock is taken before the debugFS functions
starts iterating the VCAP rules.
It also adds a separate function to decode a rule, which expects the lock
to have been taken before it is called.

Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>