Most controllers require the direction of a GPIO to be set by writing to
a direction register.  Add support for either an input direction
register or an output direction 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>