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/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index 4b97df3..4fee6db 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -23,3 +23,4 @@
 obj-$(CONFIG_BCM2835_WDT)       += bcm2835_wdt.o
 obj-$(CONFIG_WDT_ORION) += orion_wdt.o
 obj-$(CONFIG_WDT_CDNS) += cdns_wdt.o
+obj-$(CONFIG_MPC8xx_WATCHDOG) += mpc8xx_wdt.o