gl-renderer: Use EGL_KHR_no_config_context

This patch makes use of recently implemented
EGL_KHR_no_config_context extension in Mesa,
which superseeds EGL_MESA_configless_context.

See also (and the follow-up patch):

https://lists.freedesktop.org/archives/mesa-dev/2016-September/128510.html

v2:

 - Extend existing infrastructure for EGL_MESA_configless_context
   per suggestion from Emmanuel Gil Peyrot.

Signed-off-by: Armin Krezović <krezovic.armin@gmail.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
diff --git a/libweston/weston-egl-ext.h b/libweston/weston-egl-ext.h
index 70556fd..f3e6dce 100644
--- a/libweston/weston-egl-ext.h
+++ b/libweston/weston-egl-ext.h
@@ -135,6 +135,10 @@
 #define EGL_NO_CONFIG_MESA                      ((EGLConfig)0)
 #endif
 
+#ifndef EGL_NO_CONFIG_KHR
+#define EGL_NO_CONFIG_KHR ((EGLConfig)0)
+#endif
+
 #ifndef EGL_EXT_platform_base
 #define EGL_EXT_platform_base 1
 typedef EGLDisplay (EGLAPIENTRYP PFNEGLGETPLATFORMDISPLAYEXTPROC) (EGLenum platform, void *native_display, const EGLint *attrib_list);