Initial setup of TISNUM register for DUALNUM mode.

  TILE-Gx don't have full hard-float FPU, while it's lukcy that
  LuaJIT VM could use either double float or integer to hold a
  number type. Thus, we need to implement DUALNUM mode for
  TILE-Gx, and use integer type as number type holder for TILE-Gx to
  cut off any unncessary float operations.