[devices]: xcvrd OIR support for Dell S6100/Z9100 switches (#2281)

* xcvrd OIR support for Dell S6100/Z9100 switches

Introduced check_interrupts function to handle missed interrupts.
port_dict updated and returned for appropriate OIR events.
Added support for both S6100/Z9100 switches.

* Revamped sfputil.py for PEP8 Standards

Author: paavaanan