mhi_bus: dev: uci: add user space interface driver

This module allows user space clients to transfer data
between external modem and host using standard file
operations.

CRs-Fixed: 2204910
Change-Id: I46af0e99a68836e50cc4da4ad3ab85e248d4af4f
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>