drm/i915: Set lvds dual channel according to register from vbios

Vbios will set lvds register correctly based on
current algorithm for lingle/dual Channel LVDS when
system boot, so we can accept this configuration
directly, regardless of LVDS enable status.

It fixed freedesktop.org bug #22262

Signed-off-by: Florian Mickler <florian@mickler.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_display.c

@@ -645,7 +645,7 @@ intel_find_best_PLL(const intel_limit_t *limit, struct drm_crtc *crtc,
 	int err = target;
 
 	if (IS_I9XX(dev) && intel_pipe_has_type(crtc, INTEL_OUTPUT_LVDS) &&
-	    (I915_READ(LVDS) & LVDS_PORT_EN) != 0) {
+	    (I915_READ(LVDS)) != 0) {
 		/*
 		 * For LVDS, if the panel is on, just rely on its current
 		 * settings for dual-channel.  We haven't figured out how to