watchdog: armada_37xx: Probe driver also when watchdog is already running

If Armada 37xx watchdog is started before U-Boot then CNTR_CTRL_ACTIVE bit
is set, U-Boot armada-37xx-wdt.c driver fails to initialize and so U-Boot
is unable to use or kick this watchdog.

Do not check for CNTR_CTRL_ACTIVE bit and always initialize watchdog. Same
behavior is implemented in Linux kernel driver.

This change allows to activate watchdog in firmware which loads U-Boot.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>