linux-imx

drm: bridge: add Cadence MHDP HDMI/DP API

Changes made in the low level driver (cdn-dp-reg.*):
- moved it to from drivers/gpu/drm/rockchip to
 drivers/gpu/drm/bridge/cadence/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: Sandor Yu <Sandor.yu@nxp.com>