mhi: dev: uci: chain large transfers together

If we're transferring a large (> mtu) packet, then chain the
descriptors together to reduce number of completion events.

CRs-Fixed: 2254571
Change-Id: I015b9b998461566541ddc1e660ccc4fc5991f84e
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>