drm/amdgpu: disallow multiple BO_HANDLES chunks in one submit

Before this commit, only submits with both a BO_HANDLES chunk and a
'bo_list_handle' would be rejected (by amdgpu_cs_parser_bos).

But if UMD sent multiple BO_HANDLES, what would happen is:
* only the last one would be really used
* all the others would leak memory as amdgpu_cs_p1_bo_handles would
  overwrite the previous p->bo_list value

This commit rejects submissions with multiple BO_HANDLES chunks to
match the implementation of the parser.

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