net: devlink: regions: Add a priv member to the regions ops struct

The driver may have multiple regions which can be dumped using one
function. However, for this to work, additional information is
needed. Add a priv member to the ops structure for the driver to use
however it likes.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>