defconfig: msm8998: Use RCU_NOCB for RCU subsystem

Use per CPU NOCB threads to process RCU callbacks, rather than processing
the callbacks in softirq context. Processing large number of callbacks
in softirq context may result in delayed execution of other softirqs, so
remove processing of callbacks from softirq context.

Change-Id: I96faf1e5c8e786a2cb2410bb1265875410f74ae3
Signed-off-by: Imran Khan <kimran@codeaurora.org>