egl/x11: Handle depth 30 drawables under software rasterizer.

For fixing eglCreateWindowSurface() under swrast, as tested
with LIBGL_ALWAYS_SOFTWARE=1.

Suggested-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>

src/egl/drivers/dri2/platform_x11.c

@@ -75,6 +75,7 @@ swrastCreateDrawable(struct dri2_egl_display * dri2_dpy,
    xcb_create_gc(dri2_dpy->conn, dri2_surf->swapgc, dri2_surf->drawable, mask, valgc);
    switch (dri2_surf->depth) {
       case 32:
+      case 30:
       case 24:
          dri2_surf->bytes_per_pixel = 4;
          break;