drm/amd/pm: correct the runpm handling for BACO supported ASIC

Via the fSMC_MSG_ArmD3 message, PMFW can properly act on the
Dstate change. Driver involvement for determining the timing for
BACO enter/exit is not needed.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>