drm/i915/icl: 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. It applies to external ports on combo phy. On
Icelake this is port A and B when those are not eDP.

v2: follow the spec to the letter: include Aux A and just check if it's
    not eDP instead of checking only for Aux B.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181012215758.25342-1-lucas.demarchi@intel.com