There's only two functions called from that:
drm_kms_helper_poll_fini() and udl_free_urb_list(). Both of these are
also called from the ubs_driver->disconnect hook, so entirely
pointless to do the same again in the ->release hook.

Furthermore by the time we clean up the drm_driver we really shouldn't
be touching hardware anymore, so stopping the poll worker and freeing
the urb allocations in ->disconnect is the right thing to do.

Now disconnect still cleans things up before unregistering the driver,
but that's a different issue.

v2: Use _fini, not _disable in unplug, motivated by discussions with
Thomas. _disable/_enable are for suspend/resume.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-51-daniel.vetter@ffwll.ch