drm/dp: Add DPCD OUI register defines

DisplayPort has an escape hatch by which sources and sinks can identify
each other.  We would prefer not to notice this, but I suspect we're
going to need to.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_dp_helper.h

@@ -213,6 +213,10 @@
 # define DP_TEST_NAK			    (1 << 1)
 # define DP_TEST_EDID_CHECKSUM_WRITE	    (1 << 2)
 
+#define DP_SOURCE_OUI			    0x300
+#define DP_SINK_OUI			    0x400
+#define DP_BRANCH_OUI			    0x500
+
 #define DP_SET_POWER                        0x600
 # define DP_SET_POWER_D0                    0x1
 # define DP_SET_POWER_D3                    0x2