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/arch/arm/cpu/arm926ejs/mx25/generic.c b/arch/arm/cpu/arm926ejs/mx25/generic.c
index 09bda0e..ef8d2d2 100644
--- a/arch/arm/cpu/arm926ejs/mx25/generic.c
+++ b/arch/arm/cpu/arm926ejs/mx25/generic.c
@@ -11,6 +11,7 @@
 #include <common.h>
 #include <clock_legacy.h>
 #include <div64.h>
+#include <net.h>
 #include <netdev.h>
 #include <vsprintf.h>
 #include <asm/io.h>