ARM: dts: msm: Enable starting PD policy engine in sdxprairie MTP

In sdxprairie, PD policy engine was disabled because the PPS portions of
the USB-PD charging standard are not supported on this platform.
Turning off the policy engine is not recommended; so, turn it back on.
With this change, USB-PD charging is able to work - but only at 5V.

Change-Id: I4609961c8ed01ca9d36a6b82c1d365aa02132094
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>