[MIPS] TXx9: cleanup and fix some sparse warnings

* Do not return void value
* Make some functions static
* Do not include unnecessary bootinfo.h

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/txx9/generic/setup.c

@@ -140,7 +140,7 @@ void __init prom_init(void)
 
 	strcpy(txx9_system_type, txx9_board_vec->system);
 
-	return txx9_board_vec->prom_init();
+	txx9_board_vec->prom_init();
 }
 
 void __init prom_free_prom_memory(void)