cleanup EGL extensions strings and entry-points

- move all the code related to EGL extensions in one place

- add missing extension strings:
   EGL_KHR_lock_surface
   EGL_KHR_reusable_sync

- add public extensions strings and entry-points
   EGL_ANDROID_wait_sync
   EGL_ANDROID_presentation_time

- add missing entry-points for EGL_KHR_reusable_sync

Change-Id: Ifd98966b549e8efd8ef5385eba0efde8c4cbc77b