drm/amdgpu: use 256 bit buffers for all wb allocations (v2)

May waste a bit of memory, but simplifies the interface
significantly.

v2: convert internal accounting to use 256bit slots

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
3 files changed