dt-bindings: display: msm/dsi: Fix the PHY regulator supply props

The PHY regulator supply names vary across different PHY versions.
Mention explicitly which PHYs require which supplies.

Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>