makedumpfile: printk: add support for lockless ringbuffer
    
    Backports:
    
    commit c617ec63339222f3a44d73e36677a9acc8954ccd
    Author: John Ogness <john.ogness@linutronix.de>
    Date:   Thu Nov 19 02:41:21 2020 +0000
    
        [PATCH 1/2] printk: add support for lockless ringbuffer
    
        * Required for kernel 5.10
    
        Linux 5.10 introduces a new lockless ringbuffer. The new ringbuffer
        is structured completely different to the previous iterations.
        Add support for retrieving the ringbuffer from debug information
        and/or using vmcoreinfo. The new ringbuffer is detected based on
        the availability of the "prb" symbol.
    
        Signed-off-by: John Ogness <john.ogness@linutronix.de>
        Signed-off-by: Kazuhito Hagio <k-hagio-ab@nec.com>
    
    Signed-off-by: Kairui Song <kasong@redhat.com>