defconfig: msm: Enable MHI device on sdxpoorwills

MHI (Modem host interface) device driver is used by
clients to transfer data between host and device over
PCIe. Software clients include QTI and software IP
clients to setup data call and transfer data.

Change-Id: I1061140397298e2dfbd24a1a4a3640fa8b34b082
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>