Patches to accommodate KBI/KPI change

[Patrick Kelsey]

__FreeBSD_version 120008 indicates that the function
smp_no_rendevous_barrier() has been renamed with the correct spelling to
smp_no_rendezvous_barrier().  This function is referenced by the ring 0
driver, and the attached patches accommodate the change.

Note that there was a gap between the commit that changed the function name
and the bump of the FreeBSD version number, so there will be build breakage
for emulators/virtualbox-ose-additions and emulators/virtualbox-ose-kmod
when building on -CURRENT r316648 through r316682, inclusive.

-Patrick