Convert the udv_lock for the list of uvm_device objects over to a mutex.
Convert the udv_lock for the list of uvm_device objects over to a mutex.

ok thib@, weingart@.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars