[Chassis] [Arista] correct platform.json for sup and LC6 names

[wenyiz2021]

for partial issues in #12590

1. Correct Arista chassis sup name to match with dut:

admin@str2-7804-sup-1:~$ show platform sum
...
Model Number: DCS-7800-SUP1A

2. add separate platform.json for LC6, which has different name bc of supporting macsec, all other infos are the same as the other 2 LC2:

admin@str2-7804-lc6-1:~$ show platform sum
Platform: x86_64-arista_7800r3_48cqm2_lc
HwSKU: Arista-7800R3-48CQM2-C48
...

Why I did it

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

Description for the changelog

Ensure to add label/tag for the feature raised. example - PR#2174 under sonic-utilities repo. where, Generic Config and Update feature has been labelled as GCU.

Link to config_db schema for YANG module changes

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

[Staphylo]

Thanks for doing this.
I will need to make some more modification to these files to make testing happy.

[wenyiz2021]

Thanks for doing this. I will need to make some more modification to these files to make testing happy.

@Staphylo not sure how much is the platform.json covered in your regression, just a kindly reminder that this won't be the final version, as psus, thermal sections also needs changes, you may want to wait after we both finalized the file.