udev: introduce CONST key name
    
    Currently, there is no way to match against system-wide constants, such
    as architecture or virtualization type, without forking helper binaries.
    That potentially results in a huge number of spawned processes which
    output always the same answer.
    
    This patch introduces a special CONST keyword which takes a hard-coded
    string as its key and returns a value assigned to that key. Currently
    implemented are CONST{arch} and CONST{virt}, which can be used to match
    against the system's architecture and virtualization type.
    
    (based on commit 4801d8afe2ff1c1c075c9f0bc5631612172e0bb7)
    
    Resolves: #1762679
    
    patch_name: 0228-udev-introduce-CONST-key-name.patch
    present_in_specfile: true
    location_in_specfile: 228
    squash_commits: true