[tilegx] Fix JS stack trace.

  kNoCodeAgeSequenceLength should be 11 for TileGX.

  Now the JS stack trace start to work. We could see something like:

  Security context: 0x5a407711 <JS Object>#0#
    1: InstallFunctions(aka InstallFunctions) [native v8natives.js:53]
    2: SetUpObject(aka SetUpObject) [native v8natives.js:1375]
    3: /* anonymous */ [native v8natives.js:1409]
[tilegx] Fix cctest compiling error.
[tilegx] Fix scratch register conflict & fp mode bug.

  * fixed one scratch register conflict bug.
  * when initialize some objects, we should mark them as kDontSaveFPRegs,
    as we don't have FPU.