watchdog: sp5100_tco: Enable watchdog on Family 17h devices if disabled

On Family 17h (Ryzen) devices, the WatchdogTmrEn bit of PmDecodeEn not only
enables watchdog memory decoding at 0xfeb00000, it also enables the
watchdog hardware itself. Use this information to enable the watchdog if
it is not already enabled.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
Link: https://lore.kernel.org/r/20200910163109.235136-2-linux@roeck-us.net


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