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/cpu/mpc8xx/Kconfig b/arch/powerpc/cpu/mpc8xx/Kconfig
index f112317..b0e90a0 100644
--- a/arch/powerpc/cpu/mpc8xx/Kconfig
+++ b/arch/powerpc/cpu/mpc8xx/Kconfig
@@ -25,6 +25,10 @@
 
 endchoice
 
+config MPC8xx_WATCHDOG
+	bool "Watchdog"
+	select HW_WATCHDOG
+
 config 8xx_GCLK_FREQ
 	int "CPU GCLK Frequency"