defconfig: mdm: Enable MHI device for MDM9650

Modem host device (MHI) driver is used to communicate
between host and device over PCIe. Clients include
QTI for software channels and IPA for hardware
accelerated channels. Enable MHI device for MDM9650.

Change-Id: I73ee11259d3fb7c835f607ecebf7a832599f0e76
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>