[WATCHDOG] at32ap700x_wdt.c - timeout module parameter patch

integrate the timeout/heartbeat as a module parameter and not as
a CONFIG_* value.

Signed-off-by: Hans-Christian Egtvedt <hcegtvedt@atmel.com>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Cc: Andrew Morton <akpm@linux-foundation.org>