drm/radeon: don't add the IB pool to all VMs v2

We want to use VMs without the IB pool in the future.

v2: also remove it from radeon_vm_finish.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>