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>

board/solidrun/clearfog/clearfog.c

@@ -6,6 +6,7 @@
 #include <common.h>
 #include <i2c.h>
 #include <miiphy.h>
+#include <net.h>
 #include <netdev.h>
 #include <asm/io.h>
 #include <asm/arch/cpu.h>

board/solidrun/mx6cuboxi/mx6cuboxi.c

@@ -15,6 +15,7 @@
 
 #include <common.h>
 #include <init.h>
+#include <net.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/iomux.h>