[Tizen] Add the EGL backend in VAVDA for Tizen Mobile.

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.

Refer to "https://codereview.chromium.org/43283002/" for more
 details. 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.
Merge pull request #86 from zhang-qing/master2.2

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