drm/i2c/ch7006: Constify ch7006_tv_norms[] and ch7006_modes[]

 drivers/gpu/drm/i2c/ch7006.ko:
-.text                        5913
+.text                        5897
-.rodata                       664
+.rodata                      7256
-.data                        6992
+.data                         416

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>