mhi_dev: mhi: select PCIe interface for MHI on MDM9630

PCIe endpoint driver provides a service layer where PCIe client
drivers can choose PCIe interface to use. Update MHI driver to
choose PCIe interface when using PCIe driver APIs.

Change-Id: Ic64b0ff77505a49b26ff8bc686bbc7d0a73c4678
Signed-off-by: Yan He <yanhe@codeaurora.org>