[Tizen] part-2 add EGL backend in VAVDA for Tizen


Why we need to maintain it in our side:

1) Upstream confirm VAVDA will continue to be restricted to
   CrOS/X86 for dev & testing only and not for chromium road map.
2) CrOS/X86 no plan to expend EGL backend which finalize in
   June 2012 and be addressed to the CrOS graphics team.

So, the upstream no plan to lerage VAVDA with EGL graphic
   backend for any X86.

3) The tizen-mobile's driver only support EGL as texture
   backend. The video hw acceleration of xwalk have to
   rely on EGL not GLX to bind decoded pixmap.

That's why we enable specific EGL for VAVDA in tizen port.