watchdog: Remove ARCH_KIRKWOOD dependency

mach-kirkwood has been removed, now that kirkwood lives in mach-mvebu.
ARCH_MVEBU is sufficient.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: linux-watchdog@vger.kernel.org
Link: https://lkml.kernel.org/r/1409417172-6846-7-git-send-email-andrew@lunn.ch


Signed-off-by: Jason Cooper <jason@lakedaemon.net>