powerpc: mpc8xx: move watchdog into drivers/watchdog

In preparation of DM watchdog, move basic actions into drivers/watchdog

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index af45cfe..13a7956 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -34,7 +34,7 @@
 	bool "MPC8xx"
 	select BOARD_EARLY_INIT_F
 	imply CMD_REGINFO
-	imply HW_WATCHDOG
+	imply MPC8xx_WATCHDOG
 
 endchoice