watchdog: hpwdt: build hpwdt as module by default with NMI_DECODING enabled

Builds the hpwdt driver as a module by default.
If the hardware is present, the module will be loaded.
Also, if hpwdt is loaded, it will decode NMIs by default.

This has been made possible by he patches to hpwdt made by Dann Frazier
as well as related patches submitted by Don Zickus.

hpwdt only loads on hp ProLiant x86 32-bit and 64-bit platforms.

Signed-off-by: Tony Camuso <tcamuso@redhat.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>