watchdog: hpwdt (3/12): Group NMI sourcing specific items together

* Group together includes specific to NMI sourcing
* Group defines only used by NMI sourcing together
* Group declarations specific to NMI sourcing together

This gives a clean seperation of watchdog specific items and
NMI sourcing specific items (which is needed for making it
possible to build hpwdt without the NMI functionality).

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>