mhi_bus: core: Add support for MHI host interface

Modem Host Interface(MHI) is a communication protocol to be used
by the host to control and communicate with modem over a high speed
peripheral bus. This module will allow host to communicate with
external devices that support MHI protocol. Snapshot of MHI (Modem
Host Interface) driver from msm-4.14
commit_id 5af1d288611ca06423449b81d2afb68afd2b1379.

Change-Id: Ia909ebdaffb6a621fa066b711971dedb2d48a18d
Signed-off-by: Nitesh Gupta <nitegupt@codeaurora.org>