egl: Add EGL_CHROMIUM_sync_control extension.

Chromium defined a new GL extension (that isn't registered with Khronos).
We need to add an EGL extension for it, so we can migrate ChromeOS on
Intel systems to use EGL instead of GLX.

http://git.chromium.org/gitweb/?p=chromium/src/third_party/khronos.git;a=commitdiff;h=27cbfdab35c601f70aa150581ad1448d0401f447

The EGL_CHROMIUM_sync_control extension is similar to the GLX extension
OML_sync_control, but only defines one function,
eglGetSyncValuesCHROMIUM, which is equivalent to glXGetSyncValuesOML.

http://www.opengl.org/registry/specs/OML/glx_sync_control.txt

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Cc: Jamey Sharp <jamey@minilop.net>
Cc: Ian Romanick <idr@freedesktop.org>
Cc: Stéphane Marchesin <stephane.marchesin@gmail.com>