firmware: arm_ffa: Unregister bus notifier on teardown for FF-A v1.0

firmware: arm_ffa: Unregister bus notifier on teardown for FF-A v1.0

For FF-A v1.0 the driver registers a bus notifier to backfill UUID
matching, but the notifier was never unregistered on cleanup paths.
Track the registration state and unregister it during teardown and early
partition-setup failure.

Fixes: 9dd15934f60d ("firmware: arm_ffa: Move the FF-A v1.0 NULL UUID workaround to bus notifier")
Link: https://patch.msgid.link/20260428-ffa_fixes-v2-5-8595ae450034@kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>