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/sf.c b/cmd/sf.c
index 2b9c268..69e0d46 100644
--- a/cmd/sf.c
+++ b/cmd/sf.c
@@ -13,6 +13,7 @@
 #include <mapmem.h>
 #include <spi.h>
 #include <spi_flash.h>
+#include <asm/cache.h>
 #include <jffs2/jffs2.h>
 #include <linux/mtd/mtd.h>