arch: arc: do not use sleep instruction for nsim smp

It's found that in nsim_hs_smp, sometimes the cpu
doesn't response inter-core interrupt after executing sleep
instruction.

It may be a bug of nsim, but needs more time to
investigate the root of this issue.

This commit is a workround for this, as nsim is just an
instruction simulator, no direct impact.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>