drm/nouveau/bar: expose interface to bar2 teardown

Will prevent spurious MMU fault interrupts if something decides to touch
BAR1 after we've unloaded the driver.

Exposed external to BAR so that INSTMEM can use it to better control the
suspend/resume fast-path access.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
6 files changed