[y_cable][Broadcom] update the BRCM y_cable driver to release 2.0 (so…

…nic-net#263)

This release goes in sync with the following firmware version of Broadcom Y cable, which is consistent with release 8
version : { "nic": "D103.2_D208.3", "tor_a": "D308.3", "tor_b": "D308.3" }


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
to support the Y-Cable API required to support Broadcom's Y-Cable.

How Has This Been Tested?
put the changes in PMON, and all API's seem to run OK.

Signed-off-by: vaibhav-dahiya <vdahiya@microsoft.com>