drm/nouveau: make use of drm_gpuvm_range_valid()

Use drm_gpuvm_range_valid() in order to validate userspace requests.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231108001259.15123-5-dakr@redhat.com