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/esd/vme8349/vme8349.c b/board/esd/vme8349/vme8349.c
index ff81164..f54c89d 100644
--- a/board/esd/vme8349/vme8349.c
+++ b/board/esd/vme8349/vme8349.c
@@ -16,6 +16,7 @@
 #include <init.h>
 #include <ioports.h>
 #include <mpc83xx.h>
+#include <net.h>
 #include <asm/mpc8349_pci.h>
 #if defined(CONFIG_OF_LIBFDT)
 #include <linux/libfdt.h>