watchdog: hpwdt (11/12): move NMI-decoding init and exit to seperate functions

Move NMI-decoding initialisation and exit code to seperate functions so that
we can ifdef-out parts of it in the future.

Also, this is for a device, so let's use dev_info instead of printk.
    
Signed-off-by: dann frazier <dannf@hp.com>
Acked-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>