linux-phytec-ti

drm: bridge: add support for Cadence MHDP DPI/DP bridge

This adds support for Cadence MHDP DPI to DP bridge.

Basically, it takes a DPI stream as input and output it encoded in DP
format. It supports SST and MST modes.

Changes made in the low level driver (cdn-dp-reg.*):
- moved it to from drivers/gpu/drm/rockchip to
  drivers/gpu/drm/bridge/cdns-mhdp-common.c and
  include/drm/bridge/cdns-mhdp-common.h
- functions for sending/receiving commands are now public
- added functions for reading registers and link training
  adjustment

Changes made in RK's driver (cdn-dp-core.*):
- Moved audio_info and audio_pdev fields from cdn_dp_device to
  cdns_mhdp_device structure.

Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Signed-off-by: Piotr Sroka <piotrs@cadence.com>
Signed-off-by: Damian Kos <dkos@cadence.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>