drm/amdgpu: support B0&B1 external revision id for yellow carp

B0 internal rev_id is 0x01, B1 internal rev_id is 0x02.
The external rev_id for B0 and B1 is 0x20.
The original expression is not suitable for B1.

v2: squash in fix for display code (Alex)

Signed-off-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org