The mtk-sd driver requires a regulator to be present, even if it is
the "fixed" regulator.  So select REGULATOR to make it hard to build
unusable configurations.
Signed-off-by: NNeilBrown <neil@brown.name>
Reviewed-by: NChaotian Jing <chaotian.jing@mediatek.com>
Signed-off-by: NUlf Hansson <ulf.hansson@linaro.org>