defconfig: 8953: Move RCU callbacks processing to kernel threads

Under high load situations RCU callback processing adds a
significant workload to softirq. This may result in CPU
starvation for other time critical entities, waiting to run
in softirq context. This patch eanbles the kernel option
which allows to perform RCU callback processing in separate
kernel threads and thus reducing the softriq workload a lot.

Change-Id: I2f8baee5d315708c76d33490a4be1792fb3fb680
Signed-off-by: Imran Khan <kimran@codeaurora.org>