drm/i915: Drop WaIncreaseLatencyIPCEnabled/1140 for cnl

Drop WaIncreaseLatencyIPCEnabled/Display w/a #1140 for
early cnl steppings.

v2: Drop the IS_GEN9_BC() change since other related
    parts of the code also use the KBL||CFL pattern

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190503173807.10834-2-ville.syrjala@linux.intel.com