[MIPS] make mips_nmi_setup() static

This change makes the needlessly global function mips_nmi_setup() static.

Successfully build-tested using default configs for Malta, Atlas
and SEAD boards.

Runtime test successfully performed by booting the Malta 4Kc board
up to the shell prompt.
Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mips-boards/generic/init.c

@@ -226,7 +226,7 @@ void __init kgdb_config(void)
 }
 #endif
 
-void __init mips_nmi_setup(void)
+static void __init mips_nmi_setup(void)
 {
 	void *base;
 	extern char except_vec_nmi;