drm/amdgpu: move the ring type into the funcs structure (v2)

It's constant, so it doesn't make to much sense to keep it
with the variable data.

v2: update vce and uvd phys mode ring structures as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>