i2c: snapshot of work-in-progress
Importing usr.sbin/i2cscan

Change-Id: If33144ba70400d24369308b7644abefb4438c9db
usr.sbin/i2cscan: support scans using 1 byte reads

Add '-r' to probe devices using 1 byte reads instead
of 0 byte writes as 0 byte writes aren't supported on
the am335x nor the dm37xx.

Submitted Upstream: http://gnats.netbsd.org/47977

Change-Id: I11bd030e93d2eb8de02c67f263fe5da8950621f3
libi2cdriver: snapshot of work-in-progress
cat24c256: snapshot of work-in-progress