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/smc91111.h b/drivers/net/smc91111.h
index 0135427..4c3acba 100644
--- a/drivers/net/smc91111.h
+++ b/drivers/net/smc91111.h
@@ -30,6 +30,7 @@
 
 #include <asm/types.h>
 #include <config.h>
+#include <net.h>
 
 /*
  * This function may be called by the board specific initialisation code