Update to efivar 31
    
    - Work around NVMe EUI sysfs change
    - Provide some oldish version strings we should have kept.
    - lots of overflow checking on our pointer math in dp parsing
    - fix major/minor device number handling in the linux code
    - Do better formatting checks for MBR partitions
    - Fixes for gcc 7
    
    Signed-off-by: Peter Jones <pjones@redhat.com>