drm/amdgpu: pass all the sdma scheds to amdgpu_mman

drm/amdgpu: pass all the sdma scheds to amdgpu_mman

This will allow the use of all of them for clear/fill buffer
operations.
Since drm_sched_entity_init requires a scheduler array, we
store schedulers rather than rings. For the few places that need
access to a ring, we can get it from the sched using container_of.

Since the code is the same for all sdma versions, add a new
helper amdgpu_sdma_set_buffer_funcs_scheds to set buffer_funcs_scheds
based on the number of sdma instances.

Note: the new sched array is identical to the amdgpu_vm_manager one.
These 2 could be merged.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Acked-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>