drm/rockchip: Change register space names in vop2

"regs" seems to generic when there are multiple register spaces, so
rename that one to "vop". Also change "gamma_lut" to better looking
"gamma-lut".

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220511082109.1110043-3-s.hauer@pengutronix.de