watchdog/hpwdt: Advertize max_hw_heartbeat_ms

Set max_hw_heartbeat_ms instead of max_timeout so that user client can
set timeout range in excess of what the underlying hardware supports.

Signed-off-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>