instance: make sure oldpins array is available after reset

instance: make sure oldpins array is available after reset

Introduce an oldpins_array_seed() helper routine, to make sure that each
call site which checks previous pin state will find valid data. This was
not always the case after decoder reset, which released the old pin data
while applications would not call srd_inst_new() again.

Preset newly allocated arrays with the default initial pin state, allow
optional application calls to specify differing initial values (when
specified by users), and keep the current state after first data was
processed.