commit 30414f30 upstream.

Display WA #1183 was recently added to workaround
"Failures when enabling DPLL0 with eDP link rate 2.16
or 4.32 GHz and CD clock frequency 308.57 or 617.14 MHz
(CDCLK_CTL CD Frequency Select 10b or 11b) used in this
 enabling or in previous enabling."

This workaround was designed to minimize the impact only
to save the bad case with that link rates. But HW engineers
indicated that it should be safe to apply broadly, although
they were expecting the DPLL0 link rate to be unchanged on
runtime.

We need to cover 2 cases: when we are in fact enabling DPLL0
and when we are just changing the frequency with small
differences.

This is based on previous patch by Rodrigo Vivi with suggestions
from Ville Syrjälä.

Cc: Arthur J Runyan <arthur.j.runyan@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171204232210.4958-1-lucas.demarchi@intel.com
(cherry picked from commit 53421c2f)
[ Lucas: Backport to 4.15 adding back variable that has been removed on
  commits not meant to be backported ]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180102201837.6812-1-lucas.demarchi@intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>