[P3] Const related operation won't proceed const iter during prologue

[tancheng]

Const related operations, e.g., phi_const

• Requires prologue to skip the non-const operand for the first time
• May or may not consume the const queue and the arrived data on the input port, which needs manually ordering the const data inside the const queue:

  VectorCGRA/fu/single/PhiRTL.py

  Lines 96 to 100 in 9c1d72e

  	s.recv_all_val @= ((s.first & s.recv_const.val) | \
  	(~s.first & s.recv_in[s.in0_idx].val))
  	s.send_out[0].val @= s.recv_all_val
  	s.recv_in[s.in0_idx].rdy @= s.recv_all_val & s.send_out[0].rdy
  	s.recv_const.rdy @= s.recv_all_val & s.send_out[0].rdy

• This becomes more complicated when prologue is more than 1 cycle and multiple const related operations mapped on that tile