watchdog: simatic: Use idiomatic selection of P2SB

While it's pretty much theoretical to be otherwise, make sure
that P2SB is selected only for X86. This is idiomatic dependency
which is used by all others who select it. Use it for Simatic
as well.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230822141859.2139630-1-andriy.shevchenko@linux.intel.com
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/watchdog/Kconfig

@@ -1683,7 +1683,7 @@ config SIEMENS_SIMATIC_IPC_WDT
 	depends on SIEMENS_SIMATIC_IPC && PCI
 	default y
 	select WATCHDOG_CORE
-	select P2SB
+	select P2SB if X86
 	help
 	  This driver adds support for several watchdogs found in Industrial
 	  PCs from Siemens.