virglrenderer: promote get_egl_display API

This API is useful for QEMU, as it may create its own EGL context to be shared with virgl. Furthermore, it helps with usage of MR "Add VIRGL_RENDERER_D3D11_SHARE_TEXTURE (using ANGLE and D3D 11.1)" !1103 (merged).

src/virglrenderer.c

@@ -723,7 +723,7 @@ int virgl_renderer_init(void *cookie, int flags, struct virgl_renderer_callbacks
    }
 
    if (!state.winsys_initialized && !state.external_winsys_initialized &&
-       state.cbs && state.cbs->version >= 4 && state.cbs->get_egl_display) {
+       state.cbs && state.cbs->version >= 3 && state.cbs->get_egl_display) {
       void *egl_display = NULL;
 
       if (!cbs->create_gl_context || !cbs->destroy_gl_context ||