dt-bindings: mfd: ocelot: Remove unnecessary driver wording

Initially there was unnecessary verbage around "this driver" in the
documentation. It was unnecessary. Remove self references about it being a
"driver" documentation and replace it with a more detailed description
about external interfaces that are supported.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Suggested-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20221025050355.3979380-3-colin.foster@in-advantage.com