Revert "powerpc/watchdog: Don't enable interrupt on PPC64 BookE"

This reverts commit 3978bdb4

, now that
critical interrupts are properly supported on ppc64 booke.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Laurentiu Tudor <Laurentiu.Tudor@freescale.com>
Cc: Wim Van Sebroeck <wim@iguana.be>