net: mscc: ocelot: add ability to perform bulk reads

Regmap supports bulk register reads. Ocelot does not. This patch adds
support for Ocelot to invoke bulk regmap reads. That will allow any driver
that performs consecutive reads over memory regions to optimize that
access.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>