drm/amdgpu/vcn: add instance number to VCN version message

For multiple VCN instances case we get multiple lines of the same
message like below:

  amdgpu 0000:43:00.0: amdgpu: Found VCN firmware Version ENC: 1.24 DEC: 9 VEP: 0 Revision: 11
  amdgpu 0000:43:00.0: amdgpu: Found VCN firmware Version ENC: 1.24 DEC: 9 VEP: 0 Revision: 11

By adding instance number to the log message for multiple VCN instances,
each line will clearly indicate which VCN instance it refers to.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: David (Ming Qiang) Wu <David.Wu3@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>