pipeline: generate custom instruction functions

pipeline: generate custom instruction functions

Generate a C function for each custom instruction, which essentially
consolidate multiple regular instructions into a single function call.
The pipeline program is split into groups of instructions, and a
custom instruction is generated for each group that has more than one
instruction. Special care is taken the instructions that can do thread
yield (RX, extern) and for those that can change the instruction
pointer (TX, near/far jump).

Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>