Why I did it
Fix an issue on the Clearwater2 linecard.
When the linecard is started with a fresh image without configuration, phys would not be initialized.
How I did it
Added default_sku for Clearwater2 which prevents config-setup from failing to create a default config_db.json.
Added some extra logic in the phy-credo-init script to run the phy_config.sh of the hwsku pointed by default_sku if the DEVICE_METADATA.localhost.hwsku information is not populated in CONFIG_DB.
How to verify it
Booting an image with this change and without configuration will lead to the phys being initialized using the phy_config.sh from default_sku.
