ARM: dts: msm: Enable MHI device for sdxpoorwills

Enable MHI (Modem host interface) for end point configuration.
MHI is used to transfer data between host and device over
PCIe.

Change-Id: I6af5eda85b670f8ce827c40f886916b09eadfd95
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>