drm/amdgpu: move IB and frame size directly into the engine description

I should have suggested that on the initial patchset. This saves us a
few CPU cycles during CS and a bunch of loc.

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>