ARC: [plat-eznps] update defconfig

Now we use default slub and not slab

Now we use nohz by default

Signed-off-by: Noam Camus <noamc@ezchip.com>
ARC: [plat-eznps] disable RCU warnings

It happens on nSIM when there is high load and CONFIG_NO_HZ_IDLE=y.
For example when running hackbench.

Maybe this is an artifact working with nSIM.

I choosed to do it inside platform and not from:
/sys/module/rcupdate/parameters/rcu_cpu_stall_suppress

Signed-off-by: Noam Camus <noamc@ezchip.com>