drm/radeon/kms: add support for hardcoded edids in rom (v2)

Some servers hardcode an edid in rom so that they will
work properly with KVMs.  This is a port of the relevant
code from the ddx.

[airlied: reworked to validate edid at boot stage - and
remove special quirk, if there is a valid EDID in the BIOS rom
we'll just try and use it.]

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_crtc.h

@@ -801,4 +801,6 @@ extern struct drm_display_mode *drm_gtf_mode(struct drm_device *dev,
 				bool interlaced, int margins);
 extern int drm_add_modes_noedid(struct drm_connector *connector,
 				int hdisplay, int vdisplay);
+
+extern bool drm_edid_is_valid(struct edid *edid);
 #endif /* __DRM_CRTC_H__ */

include/drm/drm_edid.h

@@ -201,4 +201,7 @@ struct edid {
 
 #define EDID_PRODUCT_ID(e) ((e)->prod_code[0] | ((e)->prod_code[1] << 8))
 
+/* define the number of Extension EDID block */
+#define DRM_MAX_EDID_EXT_NUM 4
+
 #endif /* __DRM_EDID_H__ */