drm/i915: Limit WaFbcHighMemBwCorruptionAvoidance to skl and bxt

Supposedly only skl/bxt need WaFbcHighMemBwCorruptionAvoidance.
Do not apply to the other gen9 platforms.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200708131223.9519-3-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>