defconfig: disable interactive governor on sdm439 target

On 4.9 kernel interactive governor is not supported instead
schedutil governor is being used.
Disable interactive governor for sdm439 target.

Change-Id: Id066dd53c71b31a7300f771f5cc04855bde7fda0
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>