drm/amdgpu: start to disentangle boco from runtime pm

BACO - Bus Active, Chip Off
BOCO - Bus Off, Chip Off

We originally only supported runtime pm on PX/HG
laptops so most of the runtime pm code looks for this.
Add a new flag to check for runtime pm enablement and
use this rather than checking for PX/HG.

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