Adding some debug when not using Switchable Graphics:

[   10.048669] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x1e
[   10.048672] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
7
[   10.048684] [drm] forcing LVDS-1 connector OFF
[   10.048721] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x20
[   10.048724] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
10
[   10.048811] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x20
[   10.048814] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
10
[   10.048877] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x21
[   10.048880] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
10
[   10.048933] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x15
[   10.048937] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
1

When using Switchable Graphics:

[   X.XXXXXXX] [drm] amdgpu_connector_add(): dp bridge encoder name: 0x1e
[   X.XXXXXXX] [drm] amdgpu_connector_add() no dp_bridge: connecter_type found:
-16345243

Then we panic/deadlock.

amdgpu_atombios_get_connector_info_from_object_table() vs
radeon_get_atom_connector_info_from_object_table()

Perhaps there's a bug in the parsing? This works fine with radeon.ko.