drm/rockchip: define gamma registers for RK3399

The VOP on RK3399 has a different approach from previous versions for
setting a gamma lookup table, using an update_gamma_lut register. As
this differs from RK3288, give RK3399 its own set of "common" register
definitions.

Signed-off-by: Hugh Cole-Baker <sigmaris@gmail.com>
Tested-by: "Milan P. Stanić" <mps@arvanta.net>
Tested-by: Linus Heckemann <git@sphalerite.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20211019215843.42718-2-sigmaris@gmail.com