watchdog: Convert ep93xx driver to watchdog core

Convert the ep93xx_wdt driver to the watchdog framework API.

Also, use the dev_<fmt> functions instead of pr_<fmt> for logging.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>