ARM: Orion: Fix WDT compile for Dove and MV78xx0

Commit 0fa1f060 (ARM: Orion: Fix
Virtual/Physical mixup with watchdog) broke the Dove & MV78xx0
build. Although these two SoC don't use the watchdog, the shared
platform code still needs to build. Add the necessary defines.

Cc: stable@vger.kernel.org
Reported-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>