mhi_bus: controller: MHI support for QCOM modems

QCOM PCIe based modems uses MHI as the communication protocol.
MHI control driver is the bus master for such modems. As the bus
master driver, it oversees power management operations
such as suspend, resume, powering on and off the device.

CRs-Fixed: 2204910
Change-Id: I836258dd3ce8d81add78915aad0c6866ce1681a5
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>