The currently hardcoded link parameters don't work on all eDP panels, so
compute the parameters at runtime depending on the mode and panel type
to allow the driver to cope with a wider variety of panels.

Note that the number of bits per pixel of the panel is still hardcoded,
but this can be addressed in a separate patch.

This is largely based on a patch by Stéphane Marchesin but the algorithm
was largely rewritten to be more readable and concise.
Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>