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/drivers/usb/host/dwc2.c b/drivers/usb/host/dwc2.c
index f25ed2d..02ca119 100644
--- a/drivers/usb/host/dwc2.c
+++ b/drivers/usb/host/dwc2.c
@@ -16,6 +16,7 @@
 #include <usb.h>
 #include <usbroothubdes.h>
 #include <wait_bit.h>
+#include <asm/cache.h>
 #include <asm/io.h>
 #include <dm/device_compat.h>
 #include <power/regulator.h>