drm/amd: add basic scheduling framework

run queue:
A set of entities scheduling commands for the same ring. It
implements the scheduling policy that selects the next entity to
emit commands from.

entity:
A scheduler entity is a wrapper around a job queue or a group of
other entities. This can be used to build hierarchies of entities.
For example all job queue entities belonging to the same process
may be placed in a higher level entity and scheduled against other
process entities.
Entities take turns emitting jobs from their job queue to the
corresponding hardware ring, in accordance with the scheduler policy.

Signed-off-by: Shaoyun Liu <Shaoyun.Liu@amd.com>
Signed-off-by: Chunming Zhou <David1.Zhou@amd.com>
Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Acked-by: Christian K?nig <christian.koenig@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>