Add basic wrapper for CK's EBR

[kmacy]

Summary

Wrapper for ck_epoch D7016

Note that this is just a prototype. Allocation waits can be made much shorter and more efficient by turning them, in effect, in to queued spinlocks.

[kmacy]

Change ebr_epoch_entry_init to never fail. Don't allocate record in defer, init should already have been called.

[• hselasky]

ebr_epoch_synchronize() can deadlock the system. Please have a look at linux_rcu.c in the LinuxKPI how to do this properly.