dt-bindings: msm: dsi: document phy-type property for 7nm dsi phy

dt-bindings: msm: dsi: document phy-type property for 7nm dsi phy

Document a new phy-type property which will be used to determine whether
the phy should operate in D-PHY or C-PHY mode.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20210617144349.28448-3-jonathan@marek.ca
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>