Refactor Linux packaging to support host-device split architecture

 Restructured packaging code to properly support host-device split packaging
   for multi-arch (kpack) builds. Extracted DEB and RPM logic into separate
   modules for better maintainability.

   Key improvements:
   - Implemented host-device package variant builder for gfxarch packages
     * Host packages contain generic/architecture-independent artifacts
     * Device packages contain architecture-specific artifacts per target
     * Meta packages depend on host + all device packages
     * Non-versioned packages provide user-facing entry point
   - Split DEB creation logic into deb_package.py (440 lines)
   - Split RPM creation logic into rpm_package.py (256 lines)
   - Refactored build_package.py to orchestrate package variants (929 lines reduced)
   - Enhanced packaging_utils.py with improved variant handling
   - Introduced build_package_variants() as unified entry point
   - Each package variant uses isolated build directory to prevent collisions

   This refactoring enables proper multi-arch packaging with clean separation
   between host and device components, improving package management for
   heterogeneous GPU environments.

Author: raramakr