Documentation/gpu: Add explanation about AMD Pipes and Queues

Documentation/gpu: Add explanation about AMD Pipes and Queues

Pipes and Queues are two common vocabulary that pervades discussions
around amdgpu core features. The definition and explanation of those
components are spread around multiple places in the code, mailing list,
and Gitlab, which sometimes leads to the wrong interpretation of these
concepts. This commit attempts to centralize the definition and
explanation of Pipe and Queue from amdgpu perspective in a kernel doc.
Most of the information in this doc was derived from:

- https://lore.kernel.org/amd-gfx/CADnq5_Pcz2x4aJzKbVrN3jsZhD6sTydtDw=6PaN4O3m4t+Grtg@mail.gmail.com/T/#m9a670b55ab20e0f7c46c80f802a0a4be255a719d
- https://gitlab.freedesktop.org/mesa/mesa/-/issues/11759

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Rodrigo Siqueira <siqueira@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>