drm/amdgpu: add irq sources for vcn v2_0 (v2)

Add the interrupt source packet definitions.

v2: update (Alex)

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Jack Xiao <Jack.Xiao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>