drm/nouveau: use GPUVM common infrastructure

GPUVM provides common infrastructure to track external and evicted GEM
objects as well as locking and validation helpers.

Especially external and evicted object tracking is a huge improvement
compared to the current brute force approach of iterating all mappings
in order to lock and validate the GPUVM's GEM objects. Hence, make us of
it.

Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231113221202.7203-1-dakr@redhat.com