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/qualcomm/dragonboard410c/dragonboard410c.c b/board/qualcomm/dragonboard410c/dragonboard410c.c
index 81bd8bd..75505d0 100644
--- a/board/qualcomm/dragonboard410c/dragonboard410c.c
+++ b/board/qualcomm/dragonboard410c/dragonboard410c.c
@@ -10,7 +10,9 @@
 #include <dm.h>
 #include <env.h>
 #include <init.h>
+#include <net.h>
 #include <usb.h>
+#include <asm/cache.h>
 #include <asm/gpio.h>
 #include <fdt_support.h>
 #include <asm/arch/dram.h>