To support AMD Adaptive Backlight Management (ABM) for power profiles daemon >= 2.0

[You-Sheng Yang]

[SRU Justification]

[Impact]

power-profiles-daemon >= 2.0 now utilizes AMD GPU panel_power_savings
sysfs entry to set desired panel power saving level. Related kernel
fixes are to be released in v6.9.

[Fix]

Two linux-next committed fixes are required. The first one introduces
panel_power_savings sysfs entry itself, and the second one extends
abmlevel sysfs entry to allow an auto mode.

[Test Case]

1. Check existence of panel_power_savings sysfs entry:

   $ cat /sys/class/drm/card0-eDP-1/amdgpu/panel_power_savings
   -1

2. Remove power cable and switch between power profiles from Power
Management settings. The content of above panel_power_savings sysfs
entry should be updated correspondingly.

[Where problems could occur]

While the abmlevel entry now has a different default value that allows
automatic power management, the behavior may differ from users'
expectation.

[Other Info]

power-profiles-daemon >= 0.20 is only available on Noble or later at
this moment, so only Noble/Unstable will be nominated for fix.

========== original bug report ==========

Required kernel fixes (in linux-next):
* https://gitlab.freedesktop.org/agd5f/linux/-/commit/63d0b87213a0ba241b3fcfba3fe7b0aed0cd1cc5
* https://gitlab.freedesktop.org/agd5f/linux/-/commit/040fdcde288a2830edc31dd507963d6aadf990d2

See also power-profiles-daemon merge request https://gitlab.freedesktop.org/upower/power-profiles-daemon/-/merge_requests/137

[You-Sheng Yang (vicamo)]

SRU:
* https://lists.ubuntu.com/archives/kernel-team/2024-March/149487.html (noble)
* https://kernel.ubuntu.com/gitea/kernel/noble-linux-unstable/src/branch/vicamo/bug-2056716-amdgpu-abm (unstable, to create PR when base branch is synced)

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux/6.8.0-32.32 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-noble-linux' to 'verification-done-noble-linux'. If the problem still exists, change the tag 'verification-needed-noble-linux' to 'verification-failed-noble-linux'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!