ARM: OMAP2+: Remove unused legacy code for watchdog

We are now booting all mach-omap2 in device tree only mode.
Any code that is only called in legacy boot mode where
of_have_populated_dt() is not set is safe to remove now.

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>