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/ccv/xpress/xpress.c b/board/ccv/xpress/xpress.c
index 0caeea5..dc86d43 100644
--- a/board/ccv/xpress/xpress.c
+++ b/board/ccv/xpress/xpress.c
@@ -4,6 +4,7 @@
  */
 
 #include <init.h>
+#include <net.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/iomux.h>
 #include <asm/arch/imx-regs.h>