watchdog: ImgTec PDC Watchdog Timer Driver

This commit adds support for ImgTec PowerDown Controller Watchdog Timer.

Reviewed-by: Andrew Bresticker <abrestic@chromium.org>
Signed-off-by: Naidu Tellapati <Naidu.Tellapati@imgtec.com>
Signed-off-by: Jude Abraham <Jude.Abraham@imgtec.com>
[ezequiel: Minor style fixes]
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>