defconfig: msm8916: Enable IDLETIMER

For fast dormancy feature, network idle timer support is required
where in timer expires and which triggers a sysfs notification.
If a matching packet is received then timer is reset. This
support is required in the kernel so enabling the config.

Change-Id: I8628fc9fa283e382b48924059390d920884cf4cf
Signed-off-by: Bhavya Sokke Mallikarjunappa <bsokke@codeaurora.org>