vgabios: Create clext.h and use "clext_" as prefix for exported funcs.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
diff --git a/vgasrc/clext.h b/vgasrc/clext.h
new file mode 100644
index 0000000..7d486a3
--- /dev/null
+++ b/vgasrc/clext.h
@@ -0,0 +1,9 @@
+#ifndef __CLEXT_H
+#define __CLEXT_H
+
+#include "types.h" // u8
+
+int clext_set_video_mode(u8 mode, u8 noclearmem);
+void clext_init(void);
+
+#endif // clext.h