iommu/vt-d: Remove unnecessary rcu_read_locks

We use RCU's for rarely updated lists like iommus, rmrr, atsr units.

I'm not sure why domain_remove_dev_info() in domain_exit() was surrounded
by rcu_read_lock. Lock was present before refactoring in d160aca5,
but it was related to rcu list, not domain_remove_dev_info function.

dmar_remove_one_dev_info() doesn't touch any of those lists, so it doesn't
require a lock. In fact it is called 6 times without it anyway.

Fixes: d160aca5 ("iommu/vt-d: Unify domain->iommu attach/detachment")

Signed-off-by: Lukasz Odzioba <lukasz.odzioba@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>