drm/amdgpu: Use logical ids for VCN/JPEG v4.0.3

Address VCN/JPEG instances using logical ids. Whenever register access is
required, get the physical instance using GET_INST.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Tested-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>