[Y-Cable][Credo] Credo implementation of YCable class which inherits …

…from YCableBase required for Y-Cable API's in sonic-platform-daemons (#203)

This PR adds support for YCable class required for platform-daemons to use the YCable API's for credo.

Description
Basically a vendor specific implementation of abstract YCableBase class .
detailed design discussion can be found https://github.com/Azure/SONiC/pull/757/files

Motivation and Context
Required for transitioning to vendor agnostic API's to be called by xcvrd, so that all types of cables can be called.

How Has This Been Tested?
Ran the changes on Arista7050cx3 switch, making changes inside the container.

Co-authored-by: xinyu <xinyu0123@gmail.com>