ARC: nSIM: fix missing core numbers for mdb-hw runner args

We don't set core numbers for mdb-hw runner for nSIM
board, so it defaults to 1, so mdb-hw runner doesn't work with
SMP boards.

Fix that.

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>