drm/amdgpu: update kernel vcn ring test

add session context buffer to decoder ring test for vcn v1 to v3.

v3 - correct the cmd for sesssion ctx buf
v2 - add the buffer into IB (Leo liu)

Signed-off-by: Saleemkhan Jamadar <saleemkhan.jamadar@amd.com>
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>