drm/amdgpu: use runpm flag rather than fbcon for kfd runtime suspend (v2)

the flag used by kfd is not actually related to fbcon, it just happens
to align.  Use the runpm flag instead so that we can decouple it from
the fbcon flag.

v2: fix resume as well

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Acked-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>