drm: radeon: remove dead code and pointless local lut storage

The redundant fb helpers .load_lut, .gamma_set and .gamma_get are
no longer used. Remove the dead code and hook up the crtc .gamma_set
to use the crtc gamma_store directly instead of duplicating that
info locally.

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Peter Rosin <peda@axentia.se>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170713162538.22788-13-peda@axentia.se

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -2217,7 +2217,6 @@ static const struct drm_crtc_helper_funcs atombios_helper_funcs = {
 	.mode_set_base_atomic = atombios_crtc_set_base_atomic,
 	.prepare = atombios_crtc_prepare,
 	.commit = atombios_crtc_commit,
-	.load_lut = radeon_crtc_load_lut,
 	.disable = atombios_crtc_disable,
 };