Add amdgpu_queue_mgr, a mechanism that allows disjointing usermode's
ring ids from the kernel's ring ids.

The queue manager maintains a per-file descriptor map of user ring ids
to amdgpu_ring pointers. Once a map is created it is permanent (this is
required to maintain FIFO execution guarantees for a context's ring).

Different queue map policies can be configured for each HW IP.
Currently all HW IPs use the identity mapper, i.e. kernel ring id is
equal to the user ring id.

The purpose of this mechanism is to distribute the load across multiple
queues more effectively for HW IPs that support multiple rings.
Userspace clients are unable to check whether a specific resource is in
use by a different client. Therefore, it is up to the kernel driver to
make the optimal choice.

v2: remove amdgpu_queue_mapper_funcs
v3: made amdgpu_queue_mgr per context instead of per-fd
v4: add context_put on error paths
v5: rebase and include new IPs UVD_ENC & VCN_*
v6: drop unused amdgpu_ring_is_valid_index (Alex)
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAndres Rodriguez <andresx7@gmail.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>