drm/amdgpu/ring: add no_scheduler flag

This allows IPs to flag whether a specific ring requires
a GPU scheduler or not.  E.g., sometimes instances of an
IP are asymmetric and have different capabilities.

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