kernel: rcu: Panic on RCU stall

Enable panic on RCU stalls if the RCU_PANIC_ON_STALL is enabled. This
helps collecting the cpu context for debugging.

Change-Id: Ibc95799df995bf31053152ab9b3894710fcd9f43
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>