egl: Add support for EGL_MESA_drm_display.

The extension defines eglGetDRMDisplay that creates an EGLDisplay from a
DRM fd.  Calling eglCreateWindowSurace or eglCreatePixmapSurface with
such displays will generate EGL_BAD_NATIVE_WINDOW or
EGL_BAD_NATIVE_PIXMAP.

src/egl/main/egldisplay.h

@@ -51,6 +51,7 @@ struct _egl_extensions
 {
    EGLBoolean MESA_screen_surface;
    EGLBoolean MESA_copy_context;
+   EGLBoolean MESA_drm_display;
    EGLBoolean KHR_image_base;
    EGLBoolean KHR_image_pixmap;
    EGLBoolean KHR_vg_parent_image;