defconfig: msm: Use RCU_BOOST option for msm8917/37/53

Use RCU_BOOST option to expedite completion of RCU read critical
sections. We are using RCU_BOOST in conjunction with RCU_NOCB
approach. The RCU_NOCB approach makes sure that the call back
processing does not starve other tasks which are in need of CPU,
while RCU_BOOST option ensures that we don't suffer from long
grace periods.

Change-Id: If82bd890eda71f0850ebb294b52f86cc42b3ff97
Signed-off-by: Imran Khan <kimran@codeaurora.org>