cleanup_tis() -> tpm_remove_hardware() -> syncrhonize_rcu() is being
called in an atomic context (tis_lock spinlock held), which is not
allowed. Convert tis_lock to mutex.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Tested-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Acked-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>