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/seco/mx6quq7/mx6quq7.c b/board/seco/mx6quq7/mx6quq7.c
index fabc348..b8aa0e7 100644
--- a/board/seco/mx6quq7/mx6quq7.c
+++ b/board/seco/mx6quq7/mx6quq7.c
@@ -8,6 +8,7 @@
  */
 
 #include <init.h>
+#include <net.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/iomux.h>