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/riscv/cpu/ax25/cache.c b/arch/riscv/cpu/ax25/cache.c
index 9df629d..35f23c7 100644
--- a/arch/riscv/cpu/ax25/cache.c
+++ b/arch/riscv/cpu/ax25/cache.c
@@ -7,6 +7,7 @@
 #include <common.h>
 #include <cpu_func.h>
 #include <dm.h>
+#include <asm/cache.h>
 #include <dm/uclass-internal.h>
 #include <cache.h>
 #include <asm/csr.h>