common: Move reset_phy() to net.h

This is a network function so let's move it into that header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/LaCie/net2big_v2/net2big_v2.c b/board/LaCie/net2big_v2/net2big_v2.c
index 686608d..5030565 100644
--- a/board/LaCie/net2big_v2/net2big_v2.c
+++ b/board/LaCie/net2big_v2/net2big_v2.c
@@ -12,6 +12,7 @@
 #include <command.h>
 #include <env.h>
 #include <i2c.h>
+#include <net.h>
 #include <asm/mach-types.h>
 #include <asm/arch/cpu.h>
 #include <asm/arch/soc.h>