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Use a hardwired L.NOP instruction from the OpenRISC reset
vector as a way to check if the workaround is necessary.
Because these L.NOP instructions are guaranteed to be there
and are read-only, this is the most reliable non-invasive test.

Reading SID would be less reliable because it is one-time
programmable and theoretically may be set to zero on some boards.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>