drm/ttm: wire up the new pool as default one v2

Provide the necessary parameters by all drivers and use the new pool alloc
when no driver specific function is provided.

v2: fix the GEM VRAM helpers

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Madhav Chauhan <madhav.chauhan@amd.com>
Tested-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.freedesktop.org/patch/397081/?series=83051&rev=1