Introduce new compatible strings for the top level MDSS wrapper device,
and the MDP5 device.

Previously, the "qcom,mdp5" and "qcom,mdss_mdp" compatible strings
were used to match the top level platform_device (which was also tied
to the top level drm_device struct). Now, these strings are used
to match the MDP5 platform device.

Use "qcom,mdss" as the compatible string for top level MDSS device.
This is now used to match the top level platform_device (which is
tied to the drm_device struct).
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>