drm/amd/display: Add an HPD filter for HDMI

drm/amd/display: Add an HPD filter for HDMI

[Why]
Some monitors perform rapid “autoscan” HPD re‑assertions right after a
disconnect or powersaving mode enablement. These appear as a quick
disconnect→reconnect with an identical EDID. Since Linux has no HDMI
hotplug detection (HPD) filter, these quick reconnects are seen as hotplug
events, which can unintentionally wake a system with DPMS off.

An example: https://gitlab.freedesktop.org/drm/amd/-/issues/2876

Such 'fake reconnects' are considered when the interval between a
disconnect and a connect is within 1500ms (experimentally chosen using
several monitors), and the two connections have the same EDID.

[How]
Implement a time-based debounce mechanism:

1. On HDMI disconnect detection, instead of immediately processing the
HPD event, save the current sink and schedule delayed work (default 1500ms)

2. If another HDMI disconnect HPD event arrives during the debounce period,
it reschedules the pending work, ensuring only the final state is processed.

3. When the debounce timer expires, re-detect the display and compare the
new sink with the cached one using EDID comparison.

4. If sinks match (same EDID), this was a spontaneous HPD toggle:
   - Update connector state internally
   - Skip hotplug event to prevent desktop rearrangement

   If sinks differ, this was a real display change:
   - Process normally with the hotplug event

The debounce delay is configurable via module parameter
'hdmi_hpd_debounce_delay_ms'.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/2876
Reviewed-by: Sun peng (Leo) Li <sunpeng.li@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit c918e75e1ed95be76f8e3156a411188f650fe03f)