drm/amd/display: Simplify brightness initialization

stable inclusion
from stable-v6.6.5
commit d05614ebad8c2eff20f40ca1f55e36a76d4b0dd8
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8N21P

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d05614ebad8c2eff20f40ca1f55e36a76d4b0dd8



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[ Upstream commit d9e865826c202b262f9ee3f17a03cc4ac5d44ced ]

[Why]
Remove the brightness cache in DC. It uses a single value to represent
the brightness for both SDR and HDR mode. This leads to flash in HDR
on/off. It also unconditionally programs brightness as in HDR mode. This
may introduce garbage on SDR mode in miniLED panel.

[How]
Simplify the initialization flow by removing the DC cache and taking
what panel has as default. Expand the mechanism for PWM to DPCD Aux to
restore cached brightness value generally.

Cc: stable@vger.kernel.org # 6.1+
Reviewed-by: Krunoslav Kovac <krunoslav.kovac@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Camille Cho <camille.cho@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>