drm/amdgpu/atpx: track whether if this is a hybrid graphics platform

hybrid graphics in this case refers to systems which use the new
platform d3 cold ACPI methods as opposed to ATPX for dGPU power
control.

Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>