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/mach-omap2/am33xx/board.c b/arch/arm/mach-omap2/am33xx/board.c
index 283f735..533601e 100644
--- a/arch/arm/mach-omap2/am33xx/board.c
+++ b/arch/arm/mach-omap2/am33xx/board.c
@@ -12,6 +12,7 @@
 #include <debug_uart.h>
 #include <errno.h>
 #include <init.h>
+#include <net.h>
 #include <ns16550.h>
 #include <spl.h>
 #include <asm/arch/cpu.h>