arm64: dts: qcom: sm8250: remove mmcx regulator

Switch dispcc and videocc into using MMCX domain directly. Drop the now
unused mmcx regulator.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210829154757.784699-7-dmitry.baryshkov@linaro.org