greybus: interface: make attributes type dependent

Make most interface attributes type dependent (e.g only UniPro and
Greybus interfaces should have a DDBL1 Manufacturer ID attribute).

Note that the power attributes (e.g. current_now) will only be visible
for UniPro- and Greybus-type interfaces (i.e. interfaces that can draw
power).

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>