mmc: mmci: Mark the DT bindings for highspeed mode as deprecated

The common mmc DT parser supports bindings for highspeed mode, thus
there are no need for mmci to provide it's own versions for these. Mark
them as deprecated in the documentation.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>