net: mscc: ocelot: expose ocelot_reset routine

Resetting the switch core is the same whether it is done internally or
externally. Move this routine to the ocelot library so it can be used by
other drivers.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Vladimir Oltean <vladimir.oltean@nxp.com> # regression
Signed-off-by: Jakub Kicinski <kuba@kernel.org>