MHDP: Adding bus format & pixel format support

[tomba]

To support multiple input and output formats, we need to use bus format negotiation. However, there are some complications:

• J7 HW has a DP wrapper, and that wrapper only supports 30 and 36 bits, and needs to be configured accordingly. (default 36 bits)
• bus format negotiation doesn't got all the way to the crtc, but ends at the first bridge. We need to pick a suitable format and configure it in the crtc. Or somehow do that via the encoder. Or add a "pseudo-bridge" for the crtc as suggested by Laurent.
• We need to figure out how MHDP behaves with bpc upscaling/downscaling. Can it send RGB 12 bpc if it receives RGB 8 bpc? Etc.

[milindcdns]

All DP formats are not supported in current DRM framework and hence bus negotiations will not be supported
Adding only the changes for new connector model.