egl: add EGL_TEXTURE_EXTERNAL_WL

Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>
eglQueryWaylandBufferWL: return EGL_TEXTURE_EXTERNAL_WL by default

Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>
Merge pull request #136 from groleo/master

use EGL_TEXTURE_EXTERNAL_WL