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/mpc837xemds/mpc837xemds.c b/board/freescale/mpc837xemds/mpc837xemds.c
index 1ae2308..90e9539 100644
--- a/board/freescale/mpc837xemds/mpc837xemds.c
+++ b/board/freescale/mpc837xemds/mpc837xemds.c
@@ -8,6 +8,7 @@
 #include <hwconfig.h>
 #include <i2c.h>
 #include <init.h>
+#include <net.h>
 #include <asm/io.h>
 #include <asm/fsl_mpc83xx_serdes.h>
 #include <spd_sdram.h>