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>

common/bootm.c

@@ -15,6 +15,8 @@
 #include <lmb.h>
 #include <malloc.h>
 #include <mapmem.h>
+#include <net.h>
+#include <asm/cache.h>
 #include <asm/io.h>
 #if defined(CONFIG_CMD_USB)
 #include <usb.h>