drm/i915: Only wait for required lanes in vlv_wait_port_ready()

Currently vlv_wait_port_ready() waits for all four lanes on the
appropriate channel. This no longer works on CHV when the unused
lanes may be power gated. So pass in a mask of lanes that the
caller is expecting to be ready.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Deepak <S&lt;deepak.s@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>