drm/amdgpu: move buffer funcs setting up a level

drm/amdgpu: move buffer funcs setting up a level

Rather than doing this in the IP code for the SDMA paging
engine, move it up to the core device level init level.
This should fix the scheduler init ordering.

v2: drop extra parens
v3: drop SDMA helpers
v4: Added a Fixes tag because amdgpu dereferences an uninitialized
    scheduler without this patch, and this patch fixes this. (Luben)

Tested-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://lore.kernel.org/r/20231025171928.3318505-1-alexander.deucher@amd.com
Acked-by: Christian König <christian.koenig@amd.com>
Fixes: 56e449603f0ac5 ("drm/sched: Convert the GPU scheduler to variable number of run-queues")
Signed-off-by: Luben Tuikov <ltuikov89@gmail.com>