cell: implement function calls from shader code. fslight demo runs now.

cell: implement function calls from shader code.  fslight demo runs now.

Used for SIN, COS, EXP2, LOG2, POW instructions.  TEX next.

Fixed some bugs in MIN, MAX, DP3, DP4, DPH instructions.

In rtasm code:
  Special-case spe_lqd(), spe_stqd() functions so they take byte offsets but
  low-order 4 bits are shifted out.  This makes things consistant with SPU
  assembly language conventions.
  Added spe_get_registers_used() function.