pipeline: introduce SWX extern instruction
pipeline: introduce SWX extern instruction

The extern instruction calls one of the member functions of a given
extern object or it calls the given extern function. The function
arguments must be written in advance to the mailbox. The results
are available in the same place after execution.

Signed-off-by: Cristian Dumitrescu <25468b8a3698eeb3c368247f8635924bb4a1ce2c@intel.com>

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