Explicitly cast some switch parameters to enum
    
    This patch is not trying to fix every switch, just the ones I worked
    with last time, because some of these were especially unreadable.
    Covers enums virDomainGraphicsType and virDomainChrType (where
    applicable).
    
    Also sort its cases by their value.
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>