Allow user static stateful functions to have IO regs turned when used in pipelines

[JulianKemmerer]

ex.

Image a pipeline of static func stages only - no room for pipelining in comb. logic as is.

Instead of dropping pipeline regs attempted to added into static funcs, turn on either input or output regs... like multipliers, allow multiple sets of input and output regs turned on too

[JulianKemmerer]

#pragma PART "xc7a35ticsg324-1l" 
#include "uintN_t.h"
uint32_t accum(uint32_t x){
  static uint32_t sum;
  sum += x;
  return sum;
}
#pragma MAIN_MHZ main 200.0
uint32_t main(uint32_t x)
{
  uint32_t i;
  for (i = 0; i < 10; i+=1)
  {
    x = accum(x);
  }
  return x;
}

should be able to make each accum() a single stage via auto pipelining