davinci: Add watchdog base address flexibility

The watchdog code currently hardcodes the base address
of the timer its using.  To support new SoCs, make it
support timers at any address.  Use the soc_info structure
to do this.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>