Revert "Revert "defconfig: enable cgroup timer slack""

This reverts commit c87ec52add2c69b66c1a1eda9b724131cdebaa3f.
Revert "Revert "fs: jbd2: backport from aosp-common-3.4-kernel (johnnyslt)""

This reverts commit 064b37f070049c14d6038a69ec1fab9767322089.