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/cmd/nand.c b/cmd/nand.c
index 4de6892..9c2b5d7 100644
--- a/cmd/nand.c
+++ b/cmd/nand.c
@@ -21,6 +21,7 @@
 
 #include <common.h>
 #include <image.h>
+#include <asm/cache.h>
 #include <linux/mtd/mtd.h>
 #include <command.h>
 #include <console.h>