common: Drop net.h from common header

Move this header out of the common header. Network support is used in
quite a few places but it still does not warrant blanket inclusion.

Note that this net.h header itself has quite a lot in it. It could be
split into the driver-mode support, functions, structures, checksumming,
etc.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/freescale/ls1043aqds/eth.c b/board/freescale/ls1043aqds/eth.c
index e1919d2..b2709be 100644
--- a/board/freescale/ls1043aqds/eth.c
+++ b/board/freescale/ls1043aqds/eth.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <net.h>
 #include <asm/io.h>
 #include <netdev.h>
 #include <fdt_support.h>