drm/nouveau: nvkm/vmm: implement raw ops to manage uvmm

The new VM_BIND UAPI uses the DRM GPU VA manager to manage the VA space.
Hence, we a need a way to manipulate the MMUs page tables without going
through the internal range allocator implemented by nvkm/vmm.

This patch adds a raw interface for nvkm/vmm to pass the resposibility
for managing the address space and the corresponding map/unmap/sparse
operations to the upper layers.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230804182406.5222-11-dakr@redhat.com