sandbox: Bring back setting mon_len in global_data

This change was made for the benefit of RISC-V but broke other
architectures also. In particular, tracing cannot work without this value.
Add it back for architectures which support it.

Fixes: 3c9fc23c443 ("sandbox: don't refer to symbol _init")
Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed