drm: rcar-du: Fix build error

Select DRM_KMS_HELPER dependency.

Build error when DRM_KMS_HELPER is not selected:

drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd48): undefined reference to `drm_atomic_helper_bridge_duplicate_state'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd50): undefined reference to `drm_atomic_helper_bridge_destroy_state'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xd70): undefined reference to `drm_atomic_helper_bridge_reset'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xdc8): undefined reference to `drm_atomic_helper_connector_reset'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xde0): undefined reference to `drm_helper_probe_single_connector_modes'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xe08): undefined reference to `drm_atomic_helper_connector_duplicate_state'
drivers/gpu/drm/rcar-du/rcar_lvds.o:(.rodata+0xe10): undefined reference to `drm_atomic_helper_connector_destroy_state'

Fixes: c6a27fa ("drm: rcar-du: Convert LVDS encoder code to bridge driver")
Cc: <[email protected]>
Signed-off-by: Daniel Gomez <[email protected]>
Reviewed-by: Emil Velikov <[email protected]>
Reviewed-by: Kieran Bingham <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Signed-off-by: Laurent Pinchart <[email protected]>

Author: Daniel Gomez

drivers/gpu/drm/rcar-du/Kconfig

@@ -31,6 +31,7 @@ config DRM_RCAR_DW_HDMI
 config DRM_RCAR_LVDS
 	tristate "R-Car DU LVDS Encoder Support"
 	depends on DRM && DRM_BRIDGE && OF
+	select DRM_KMS_HELPER
 	select DRM_PANEL
 	select OF_FLATTREE
 	select OF_OVERLAY