Exclude Marvell Prestera files from main package
    
    These were meant to be split into a subpackage, but we neglected
    to include a sed command to drop them from the main package file
    list, so they wound up in *both* the main package and the sub
    package. This should drop them from the main package.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>