drm/rockchip: support gamma control on RK3399

The RK3399 has a 1024-entry gamma LUT with 10 bits per component on its
"big" VOP and a 256-entry, 8 bit per component LUT on the "little" VOP.
Compared to the RK3288, it no longer requires disabling gamma while
updating the LUT. On the RK3399, the LUT can be updated at any time as
the hardware has two LUT buffers, one can be written while the other is
in use. A swap of the buffers is triggered by writing 1 to the
update_gamma_lut register.

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/20211019215843.42718-3-sigmaris@gmail.com