drm/msm/dsi: Don't get DSI index from DT

The DSI host and PHY driver currently expects the DT bindings to provide
custom properties "qcom,dsi-host-index" and "qcom,dsi-phy-index" so that
the driver can identify which DSI instance it is.

The binding isn't acceptable, but the driver still needs to figure out
what its instance id. This is now done by storing the mmio starting
addresses for each DSI instance in every SoC version in the driver. The
driver then identifies the index number by trying to match the stored
address with comparing the resource start address we get from DT.

We don't have compatible strings for DSI PHY on each SoC, but only the
DSI PHY type. We only support one SoC version for each PHY type, so we
get away doing the same thing above for the PHY driver. We can revisit
this when we support two SoCs with the same DSI PHY.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>