watchdog: hpwdt: Update nmi_panic message.

Include the nmistat in the nmi_panic message to give support
an indication why the NMI was called (e.g. a timeout or generate
nmi button.)

Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>