defconfig: 8994: enable input devices

Enable input devices that are part of msm8994. The
list of devices enabled are

- Touch (Synaptics_dsx)
- Vibrator (PMIC HAPTICS)
- Backlight (PMIC WLED)

Change-Id: I7bc9299327021f05d6735ac5dd67c4dc7546d405
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>