vgabios: Add support for vesa get/set window function.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/vgasrc/clext.h b/vgasrc/clext.h
index 718b756..b300cf4 100644
--- a/vgasrc/clext.h
+++ b/vgasrc/clext.h
@@ -4,6 +4,8 @@
 #include "types.h" // u16
 
 struct vgamode_s *clext_find_mode(int mode);
+int clext_get_window(struct vgamode_s *vmode_g, int window);
+int clext_set_window(struct vgamode_s *vmode_g, int window, int val);
 int clext_set_mode(struct vgamode_s *vmode_g, int flags);
 void clext_list_modes(u16 seg, u16 *dest, u16 *last);
 int clext_init(void);