#### Why I did it
- xcvrd crash was seen in latest 201811 images.
- For Dell S6100,API 2.0 uses poll mode while 1.0 was still using interrupt mode.
#### How I did it
- Modified get_transceiver_change_event in 1.0 to poll mode in all the related branches.
Backport of https://github.com/Azure/sonic-buildimage/pull/7309 to the 201911 branch
* 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
( All device-specific files now reside under /device directory in a <vendor-name>/<platform-string>/<hardware-SKU> directory structure in repo.
* Device-specific files are now packaged into a Debian package (sonic-device-data) and are now installed to /usr/share/sonic/device/<platform-string>/<hardware-SKU>/ directory on switch.
