drm/msm/dsi: Hook up refgen regulator

Consume the refgen supply on configurations that may use it.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/545333/
Link: https://lore.kernel.org/r/20230628-topic-refgen-v3-4-9fbf0e605d23@linaro.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>