i2c: work in progress i2c dirver for am335x/dm37xx
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
i2c: irq enable

Change-Id: I0a22ceb447fd959249af9d53d35c0f07a6695f05