ARM: OMAP: Fix omap_wdt driver failure on 2420 when running multi-omap config

omap_wdt driver will do unhandled fault on 2420 if support for 2430 is
compiled in since wrong base address is defined in that case. Assign
omap_wdt base address runtime depending on cpu type.

Signed-off-by: Jarkko Nikula <jarkko.nikula@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>