drm: introduce HLG EOTF

CTA-861-G defined Hybrid Log-Gamma (HLG) based on ITU-R
BT.2100-0.

Change-Id: Ieb18284265529ee8d76b250d8bb5b3752425814a
Signed-off-by: Zheng Yang <zhengyang@rock-chips.com>

Author: Zheng Yang

include/uapi/drm/drm_mode.h

@@ -516,6 +516,7 @@ enum supported_eotf_type {
 	TRADITIONAL_GAMMA_SDR = 0,
 	TRADITIONAL_GAMMA_HDR,
 	SMPTE_ST2084,
+	HLG,
 	FUTURE_EOTF
 };