drm/sti: Constify function pointer structs

drm/sti: Constify function pointer structs

Moves a bunch of junk to .rodata from .data.

 drivers/gpu/drm/sti/sticompositor.ko:
-.text                       12216
+.text                       12212
-.rodata                      1284
+.rodata                      1400
-.data                         488
+.data                         372

 drivers/gpu/drm/sti/sti_drv.ko:
-.rodata                      516
+.rodata                      544
-.data                        368
+.data                        340

 drivers/gpu/drm/sti/stidvo.ko:
-.text                       3356
+.text                       3348
-.rodata                      188
+.rodata                      256
-.data                        572
+.data                        504

 drivers/gpu/drm/sti/sti_hda.ko:
-.text                       3008
+.text                       3004
-.rodata                     2820
+.rodata                     2888
-.data                        684
+.data                        616

 drivers/gpu/drm/sti/stihdmi.ko:
-.text                        6988
+.text                        6980
-.rodata                      1340
+.rodata                      1408
-.data                         176
+.data                         108

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>