drm/amdgpu: handle all fragment sizes v4

This can improve performance for some cases.

v2 (chk): handle all sizes, simplify the patch quite a bit
v3 (chk): adjust dw estimation as well
v4 (chk): use single loop, make end mask 64bit

Signed-off-by: Roger He <Hongbo.He@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Tested-by: Roger He <Hongbo.He@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>