arm64: dts: qcom: sm8250: power up dispcc on sm8250 by MMCX regulator

Add regulator controlling MMCX power domain to be used by display clock
controller on SM8250.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20201203142105.841666-8-dmitry.baryshkov@linaro.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>