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/drivers/net/fsl_enetc.c b/drivers/net/fsl_enetc.c
index bee7315..2fa27c7 100644
--- a/drivers/net/fsl_enetc.c
+++ b/drivers/net/fsl_enetc.c
@@ -9,6 +9,8 @@
 #include <errno.h>
 #include <malloc.h>
 #include <memalign.h>
+#include <net.h>
+#include <asm/cache.h>
 #include <asm/io.h>
 #include <pci.h>
 #include <miiphy.h>