drm/tegra: Constify function pointer structs

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

 drivers/gpu/drm/tegra/tegra-drm.ko:
-.rodata                     13672
+.rodata                     13684
-.data                        1108
+.data                        1096
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450178476-26284-26-git-send-email-boris.brezillon@free-electrons.comSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/tegra/fb.c

@@ -86,7 +86,7 @@ static int tegra_fb_create_handle(struct drm_framebuffer *framebuffer,
 	return drm_gem_handle_create(file, &fb->planes[0]->gem, handle);
 }
 
-static struct drm_framebuffer_funcs tegra_fb_funcs = {
+static const struct drm_framebuffer_funcs tegra_fb_funcs = {
 	.destroy = tegra_fb_destroy,
 	.create_handle = tegra_fb_create_handle,
 };