drm: Extract drm_color_mgmt.[hc]

For both the new degamm/lut/gamma atomic combo, and the old legacy
gamma tables.

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1474448370-32227-5-git-send-email-daniel.vetter@ffwll.ch