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/rockchip/tinker_rk3288/tinker-rk3288.c b/board/rockchip/tinker_rk3288/tinker-rk3288.c
index 7af39e1..f85209c 100644
--- a/board/rockchip/tinker_rk3288/tinker-rk3288.c
+++ b/board/rockchip/tinker_rk3288/tinker-rk3288.c
@@ -9,6 +9,7 @@
 #include <env.h>
 #include <i2c_eeprom.h>
 #include <init.h>
+#include <net.h>
 #include <netdev.h>
 #include <asm/arch-rockchip/bootrom.h>
 #include <asm/io.h>