[MIPS] fix sparse warning about setup_early_printk()

This patch fixes the following sparse warning:

<<<<<<<<

arch/mips/kernel/early_printk.c:35:13: warning: symbol 'setup_early_printk'
was not declared. Should it be static?

<<<<<<<<

The fix is to define a prototype of the setup_early_printk() function and
to include the appropriate header into arch/mips/kernel/early_printk.c.

[Ralf: Sorted includes again]

Signed-off-by: Dmitri Vorobiev <dmitri.vorobiev@movial.fi>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/include/asm-mips/setup.h b/include/asm-mips/setup.h
index 70009a9..883f59b 100644
--- a/include/asm-mips/setup.h
+++ b/include/asm-mips/setup.h
@@ -3,4 +3,6 @@
 
 #define COMMAND_LINE_SIZE	256
 
+extern void setup_early_printk(void);
+
 #endif /* __SETUP_H */