drm/i915/dp: Add dpcd link_rate quirk for Apple 15" MBP 2017 (v3)

drm/i915/dp: Add dpcd link_rate quirk for Apple 15" MBP 2017 (v3)

This fixes a problem found on the MacBookPro 2017 Retina panel.

The panel reports 10 bpc color depth in its EDID, and the
firmware chooses link settings at boot which support enough
bandwidth for 10 bpc (324000 kbit/sec = multiplier 0xc),
but the DP_MAX_LINK_RATE dpcd register only reports
2.7 Gbps (multiplier value 0xa) as possible, in direct
contradiction of what the firmware successfully set up.

This restricts the panel to 8 bpc, not providing the full
color depth of the panel.

This patch adds a quirk specific to the MBP 2017 15" Retina
panel to add the additiional 324000 kbps link rate during
edp setup.

Link to previous discussion of a different attempted fix
with Ville and Jani:

https://patchwork.kernel.org/patch/11325935/

v2: Follow Jani's proposal of defining quirk_rates[] instead
    of just appending 324000. This for better clarity.

v3: Rebased onto current drm-tip, as of 16-March-2020. Adapt
    to new edid_quirks parameter of drm_dp_has_quirk().

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Tested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200316042340.4783-1-mario.kleiner.de@gmail.com