drm/amdgpu: Fix size validation for non-exclusive domains (v4)

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: Fix size validation for non-exclusive domains (v4) Fix amdgpu_bo_validate_size() to check whether the TTM domain manager for the requested memory exists, else we get a kernel oops when dereferencing "man". v2: Make the patch standalone, i.e. not dependent on local patches. v3: Preserve old behaviour and just check that the manager pointer is not NULL. v4: Complain if GTT domain requested and it is uninitialized--most likely a bug.