watchdog: aspeed: Update bootstatus handling

The boot status in the watchdog device struct is updated during
controller probe stage. Application layer can get the boot status
through the command, cat /sys/class/watchdog/watchdogX/bootstatus.
The bootstatus can be,
WDIOF_CARDRESET => System is reset due to WDT timeout occurs.
Others          => Other reset events, e.g., power on reset.

On ASPEED platforms, boot status is recorded in the SCU registers.
- AST2400: Only a bit is used to represent system reset triggered by
           any WDT controller.
- AST2500/AST2600: System reset triggered by different WDT controllers
                   can be distinguished by different SCU bits.

Besides, on AST2400 and AST2500, since alternating boot event is
also triggered by using WDT timeout mechanism, it is classified
as WDIOF_CARDRESET.

Signed-off-by: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
Reviewed-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20250113093737.845097-2-chin-ting_kuo@aspeedtech.com


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