input: atmel_mxt: Add support for devices with no lpm support

Disable the regulators used by the controller when the device
does not support low power mode(lpm).

Change-Id: Ic974c7922c8888fefdfbbe1f5503f34c5964e993
Signed-off-by: Chun Zhang <chunz@codeaurora.org>
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>