watchdog: Don't select CONFIG_WATCHDOG and CONFIG_HW_WATCHDOG at the same time

Commit 06985289d452 ("watchdog: Implement generic watchdog_reset()
version") introduced an automatic selection of CONFIG_WATCHDOG by
CONFIG_WDT. But for boards selecting CONFIG_HW_WATCHDOG, like
boards have a powerpc 8xx, CONFIG_WATCHDOG shall not be selected
as they are mutually exclusive.

Make CONFIG_WATCHDOG dependent on !CONFIG_HW_WATCHDOG

Fixes: 06985289d452 ("watchdog: Implement generic watchdog_reset() version")
Cc: Stefan Roese <sr@denx.de>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
index fbb561b..d24c1e4 100644
--- a/drivers/watchdog/Kconfig
+++ b/drivers/watchdog/Kconfig
@@ -2,6 +2,7 @@
 
 config WATCHDOG
 	bool "Enable U-Boot watchdog reset"
+	depends on !HW_WATCHDOG
 	help
 	  This option enables U-Boot watchdog support where U-Boot is using
 	  watchdog_reset function to service watchdog device in U-Boot. Enable