drm/amdgpu: Fix the exported always on CU bitmap

Newer asics with 4 SEs are not able to fit the entire bitmask in the
original field, use an array instead.

v2: keep cu_ao_mask for backward compatibility.

Signed-off-by: Flora Cui <Flora.Cui@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>