drm/i915: VBT's child_device_config changes over time

We currently treat the child_device_config as a simple struct, but
this is not correct: new BDB versions change the meaning of some
offsets, so the struct needs to be adjusted for each version.

Since there are too many changes (today we're in version 170!), making
a big versioned union would be too complicated, so child_device_config
is now a union of 3 things: (i) a "raw" byte array that's safe to use
anywhere; (ii)  an "old" structure that's the one we've been using and
should be safe to keep in the SDVO and TV code; and (iii) a "common"
structure that should contain only fields that are common for all the
known VBT versions.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_lvds.c b/drivers/gpu/drm/i915/intel_lvds.c
index 639650c..67a4a8f 100644
--- a/drivers/gpu/drm/i915/intel_lvds.c
+++ b/drivers/gpu/drm/i915/intel_lvds.c
@@ -794,7 +794,8 @@
 		return true;
 
 	for (i = 0; i < dev_priv->vbt.child_dev_num; i++) {
-		struct child_device_config *child = dev_priv->vbt.child_dev + i;
+		union child_device_config *uchild = dev_priv->vbt.child_dev + i;
+		struct old_child_dev_config *child = &uchild->old;
 
 		/* If the device type is not LFP, continue.
 		 * We have to check both the new identifiers as well as the