[tilegx] Fix array allocation error in v8native.js.

  TileGX is 64bit, should use 64bit Smi representation.
[tilegx] Fix more Integer/Smi conversion.
[tilegx] Fix another issue related with Smi.

  the loop boundary is stored as Smi format.
  MIPS subtract the boundary by 1 every iteration, because
  MIPS use 32bit Smi representation, so subtract by 1 are
  calculated by "+ (-1 << 1)", for TileGX we should use
  "+ (-1 << 32)".

  We use another simpler way. Restore Smi format to normal
  integer format before we entering the loop, so the code
  could be simplified.