drm/radeon/dce8: properly handle interlaced timing

The register bits changed on DCE8 compared to previous
families.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/cik_reg.h b/drivers/gpu/drm/radeon/cik_reg.h
index b96dac0..58b29b5 100644
--- a/drivers/gpu/drm/radeon/cik_reg.h
+++ b/drivers/gpu/drm/radeon/cik_reg.h
@@ -62,4 +62,7 @@
 #define CIK_ALPHA_CONTROL                         0x6af0
 #       define CIK_CURSOR_ALPHA_BLND_ENA          (1 << 1)
 
+#define CIK_LB_DATA_FORMAT                        0x6b00
+#       define CIK_INTERLEAVE_EN                  (1 << 3)
+
 #endif