i2c driver for SiFive Unmatched

From: Thomas Skibo <thomas-bsd_at_skibo.net>
Date: Fri, 22 Oct 2021 21:05:47 UTC

I have the OpenCores i2c driver (dev/iicbus/iicoc.c) up and running on the
SiFive Unmatched.  It was just a matter of adding the right compatibility
strings and implementing iicoc_iicbus_repeated_start() which, oddly, was
stubbed out.  (Seems to me it should have returned an error if not

I can put it up on Phabricator if there is interest.

--Thomas Skibo