watchdog: renesas_wdt: support handover from bootloader

Support an already running watchdog by checking its enable bit and set
up the status accordingly before registering the device.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200908095615.31376-1-wsa+renesas@sang-engineering.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>