[Arista] Add hwsku Arista-7260CX3-G54S48 for 54x1G+48x10G

[byu343]

Why I did it

Add new hwsku Arista-7260CX3-G54S48 for the port layout 54x1G+48x10G

The 48x10G ports are from 4x10G breakout of

• Et14,45,46 (pipe 0)
• Et16,47,48 (pipe 1)
• Et18,49,50 (pipe 2)
• Et20,51,52 (pipe 3)

The 54x1G ports are from

• 52 QSA adapters on the remaining QSFP ports
• 2 SFP ports

Work item tracking

• Microsoft ADO (number only):

How I did it

Add hwsku.json, port_config.ini and config.bcm.j2 for the new port layout
The serdes tuning values are set by config.bcm.j2 for all the 10G ports assuming optical-based xcvr.
Update the breakout mode from 1x10G to 1x10G[1G] for SFP port 65, 66 in platform.json, for using SFP as 1G.

How to verify it

We verify some of the 10G ports and 1 of 1G ports based on the connectivity availability of our lab dut. They show up in 'show int st' and can pass traffic.

Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012
• 202106
• 202111
• 202205
• 202211

Tested branch (Please provide the tested image version)

Description for the changelog

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)