mmc: host: Drop unneeded MMC dependency in Kconfig

All entries in Kconfig are already part of "if MMC", so there is no need
for additional dependency on MMC.

Suggested-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200904164315.24618-1-krzk@kernel.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>