Why I did it

• SN6810_LD hardware includes a PDB, but platform.json previously had empty psus and no pdbs entry.
• Without pdbs in platform.json, DeviceDataManager.get_pdb_count() returns 0 and chassis.initialize_pdb() does not instantiate PDB objects, so PDB status/telemetry is unavailable via platform API.
• Adding PDB metadata keeps SN6810_LD consistent with other LD platforms and unblocks PDB-related monitoring and validation.

Work item tracking

• Microsoft ADO (number only):

How I did it

• Updated device/mellanox/x86_64-nvidia_sn6810_ld-r0/platform.json
• Updated device/mellanox/x86_64-nvidia_sn6810_ld_simx-r0/platform.json
• Added under chassis:

"pdbs": [
    {
        "name": "PDB 1"
    }
]

How to verify it

• Build image for x86_64-nvidia_sn6810_ld-r0 / SimX SKU
• After boot, verify PDB is initialized:
  • show platform pdb status (or equivalent platform CLI)
  • Python: sonic_platform.chassis.Chassis().get_num_pdbs() returns 1
• Confirm no regression on SimX platform bring-up

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

• 202305
• 202311
• 202405
• 202411
• 202505
• 202511

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)