drm/i915/cnl: apply Display WA #1178 to fix type C dongles

Display WA #1178 is meant to fix Aux channel voltage swing too low with
some type C dongles. Although it is for type C, HW engineers reported
that it can be applied to all external ports even if they are not going
to type C.

For CNL we apply the workaround every time Aux B, C and D are powering
up since they will lose the configuration when powered down.

v2: Use common tag for WA

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Arthur J Runyan <arthur.j.runyan@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171128220553.22435-1-lucas.demarchi@intel.com