Fixes for main

Generic Fixes:

• Update layer names for meta-secure-core
• Update LAYERSERIES_COMPAT for scarthgap
• Don't switch to root for sanity tests

KV260 Fixes:

• Drop support for 6.5 kernel in KV260

Corstone-1000 Fixes:

• Use predictable network names for Corstone-1000
• Rebase Trusted Services patch for Corstone-1000
• Fix timeout in Corstone-1000 MPS3 sanity tests
• Fix login for Corstone-1000 flash image
• Configure utils overlay image for Corstone-1000 MPS3

Notes:

• Also needs BSP changes from https://gitlab.arm.com/cassini/meta-cassini-bsp/-/merge_requests/10