drm/amdgpu: Add BRACKET_LAYOUT_ENUMs to ObjectID.h

DC has an upcoming change that requires these to read the board layout.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>