drm: drm_helper_crtc_enable_color_mgmt() => drm_crtc_enable_color_mgmt()

Add drm_crtc_enable_color_mgmt(), remove drm_helper_crtc_enable_color_mgmt()
and update drm/i915-driver (the only user of the old function).

The new function is more flexible. It allows driver to enable only the
features it has without forcing to enable all three color management
properties: degamma lut, csc matrix (ctm), and gamma lut.

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>