[Tizen] Enable NaCl/PNaCl for 32bit build

Summary of changes:
============
* Enable nacl build and packaing in crosswalk.spec
* Unify GetXWalkDataPath for Tizen (service and non-service)
* Add native_client in source tarball

How to test:
============
On linux
$ cd <nacl_sdk_dir>/pepper_canary/example
$ TOOLCHAIN=pnacl make serve

On Tizen device or VM:
$ xwalk http://<your_linux_host>:5103/demo/flock/index.html?tc=pnacl

BUG=XWALK-1339
Merge pull request #1914 from halton/nacl_tizen

[Tizen] Enable NaCl/PNaCl for 32bit build