Consolidate DisplaySurface allocation in qemu_alloc_display()

This removes various code duplication from console.e and sdl.c

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/console.h b/console.h
index f4e4741..711895e 100644
--- a/console.h
+++ b/console.h
@@ -189,6 +189,8 @@
 DisplayState *get_displaystate(void);
 DisplaySurface* qemu_create_displaysurface_from(int width, int height, int bpp,
                                                 int linesize, uint8_t *data);
+void qemu_alloc_display(DisplaySurface *surface, int width, int height,
+                        int linesize, PixelFormat pf, int newflags);
 PixelFormat qemu_different_endianness_pixelformat(int bpp);
 PixelFormat qemu_default_pixelformat(int bpp);