[WATCHDOG] mpc83xx_wdt: convert to the OF platform driver

This patch simply converts mpc83xx_wdt to the OF platform driver so we can
directly work with the device tree without passing various stuff through
platform data.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>