eal/bsd: add interrupt thread
eal/bsd: add interrupt thread

Add interrupt thread to FreeBSD. It is largely a copy-paste from
Linuxapp interrupt thread, except for a few key differences:

* Use kevent instead of epoll
* Do not recreate the event queue on adding/removing interrupt
  sources, add/remove them to/from the queue on the fly instead
* No support for UIO/VFIO handles

Signed-off-by: Anatoly Burakov <814e00d8f6e4e81b7ccc7e3e5a0bfec0078f0203@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk