ANDROID: gki_defconfig: Enable SCHED_TUNE

Seems like SCHED_TUNE would be desired in the GKI.

This is only needed on android-4.19, in future kernels the feature will
be replaced with an alternative solution.

Bug: 140203951
Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: I220ac6a2099dfd14c71b0e67fbece025b1567c8b