usb: msm_otg: Disable LPM on targets using device tree

Low power mode is not supported as of now on targets which are
using device tree. Revert this later when support is in place.

Change-Id: I05d6089d037312a0e719f4263093bde730c3a8ad
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>