Some controllers have separate input and output registers.  For these
controllers, use "set" for the output and "dat" for the input.

Changes since v2: reuse "set" for output and "dat" for input rather than
adding a new "in" register.
Signed-off-by: NJamie Iles <jamie@jamieiles.com>
Acked-by: NAnton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>