pinctrl: ocelot: add ability to be used in a non-mmio configuration

There are a few Ocelot chips that contain pinctrl logic, but can be
controlled externally. Specifically the VSC7511, 7512, 7513 and 7514. In
the externally controlled configurations these registers are not
memory-mapped.

Add support for these non-memory-mapped configurations.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220905162132.2943088-4-colin.foster@in-advantage.com