Add a new sdl2_2d_redraw function for a complete screen refresh,
so we can stop using graphic_hw_invalidate for that.  There is
no need to bother console / gfx emulation code if we are just
going to re-blit the screen after window resizes.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>