drm/amd/display: Drop dm_prepare_suspend() and dm_complete()

[Why]
dm_prepare_suspend() was added in commit 50e0bae3
("drm/amd/display: Add and use new dm_prepare_suspend() callback")
to allow display to turn off earlier in the suspend sequence.

This caused a regression that HDMI audio sometimes didn't work
properly after resume unless audio was playing during suspend.

[How]
Drop dm_prepare_suspend() callback. All code in it will still run
during dm_suspend(). Also drop unnecessary dm_complete() callback.
dm_complete() was used for failed prepare and also for any case
of successful resume.  The code in it already runs in dm_resume().

This change will introduce more time that the display is turned on
during suspend sequence. The compositor can turn it off sooner if
desired.

Cc: Harry Wentland <harry.wentland@amd.com>
Reported-by: Przemysław Kopa <prz.kopa@gmail.com>
Closes: https://lore.kernel.org/amd-gfx/1cea0d56-7739-4ad9-bf8e-c9330faea2bb@kernel.org/T/#m383d9c08397043a271b36c32b64bb80e524e4b0f


Reported-by: Kalvin <hikaph+oss@gmail.com>
Closes: https://github.com/alsa-project/alsa-lib/issues/465
Closes: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/4809


Fixes: 50e0bae3 ("drm/amd/display: Add and use new dm_prepare_suspend() callback")
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>