ptp: ocp: add .init function for sma_op vector

Create an .init function for the op vector, and a corresponding
wrapper function, for different sma mapping setups.

Add a default_fcn to the sma information, and use it when displaying
information for pins which have fixed functions.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>