common: Move mii_init() function out of common.h

This function belongs in mii.h so move it over.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/include/linux/mii.h b/include/linux/mii.h
index 21db032..49e29ac 100644
--- a/include/linux/mii.h
+++ b/include/linux/mii.h
@@ -225,4 +225,6 @@
 	return cap;
 }
 
+void mii_init(void);
+
 #endif /* __LINUX_MII_H__ */