[legal] Add a selection of FILE_LICENCE declarations

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

src/hci/mucurses/mucurses.c

@@ -8,6 +8,8 @@
  *
  */
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 static void _wupdcurs ( WINDOW *win ) __nonnull;
 void _wputch ( WINDOW *win, chtype ch, int wrap ) __nonnull;
 void _wputc ( WINDOW *win, char c, int wrap ) __nonnull;