ot1200: add feature pads

The older 'mr' variant and the generic variant of the
OT1200 differ in some places. As the name suggests the
generic variant supports more boot devices.

In order to be compatible with the 'mr' variant we define
some 'feature' GPIOs. On the 'mr' variant this pads are
not connected so we define their state with the help
of the internal pullups.

On the generic variant this GPIOs are connected and
represent the state of the hardware.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>