dt-bindings: msm: dsi: add yaml schemas for DSI PHY bindings

Add YAML schema for the device tree bindings for DSI PHY.

Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1621856653-10649-3-git-send-email-mkrishn@codeaurora.org


Signed-off-by: Rob Clark <robdclark@chromium.org>