defconfig: msm8996: 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: I90d070ad824d2df0f3e1ee29da1b48ae2887b64b
Signed-off-by: Wei Li <weili@codeaurora.org>