drm/amd/pm: fix runpm hang when amdgpu loaded prior to sound driver

Current RUNPM mechanism relies on PMFW to master the timing for BACO
in/exit. And that needs cooperation from sound driver for dstate
change notification for function 1(audio). Otherwise(on sound driver
missing), BACO cannot be kicked in correctly and hang will be observed
on RUNPM exit.

By switching back to legacy message way on sound driver missing,
we are able to fix the runpm hang observed for the scenario below:
amdgpu driver loaded -> runpm suspend kicked -> sound driver loaded

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reported-and-tested-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org