swrastg: Use new drm_driver interface in EGL

The EGL state tracker is really weird in how it does software,
in the past we would just not return a drm_api struct but now,
there is no callback to get a function so we just set the
create_screen hock to NULL to make it switch to software.

src/gallium/targets/egl-swrast/swrast_glue.c

@@ -1,10 +1,11 @@
-#include "state_tracker/drm_api.h"
 
-struct drm_api *
-drm_api_create()
-{
-   return NULL;
-}
+#include "state_tracker/drm_driver.h"
+
+struct drm_driver_descriptor drm_driver = {
+   .name = "swrast";
+   .driver_name = NULL;
+   .create_screen = NULL;
+};
 
 /* A poor man's --whole-archive for EGL drivers */
 void *_eglMain(void *);