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/freescale/ls2080aqds/eth.c b/board/freescale/ls2080aqds/eth.c
index 6a8788c..bbb70a8 100644
--- a/board/freescale/ls2080aqds/eth.c
+++ b/board/freescale/ls2080aqds/eth.c
@@ -5,6 +5,7 @@
 
 #include <common.h>
 #include <env.h>
+#include <net.h>
 #include <netdev.h>
 #include <asm/io.h>
 #include <asm/arch/fsl_serdes.h>