[CICD] Add Hygon DCU adaptation and CI workflow

[AlexMa616]

PR Category

Others

PR Types

New Features

PR Description

Add Hygon DCU support and CI integration for FlagCX.

• Add Hygon platform configuration and environment setup.
• Add a dedicated Hygon DCU unit-test workflow.
• Register Hygon in the platform registry.
• Make PR unit tests consume all enabled platforms from the registry.
• Keep common workflows vendor-neutral.
• Fix DU builds by linking the default Device API backend in makefiles/du.mk.
• Add argument validation for Hygon host-memory adaptor APIs.