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/generic/cpu.c b/arch/riscv/cpu/generic/cpu.c
index 13a69ef..d78e1a3 100644
--- a/arch/riscv/cpu/generic/cpu.c
+++ b/arch/riscv/cpu/generic/cpu.c
@@ -5,6 +5,7 @@
 
 #include <common.h>
 #include <irq_func.h>
+#include <asm/cache.h>
 
 /*
  * cleanup_before_linux() is called just before we call linux