watchdog: mpc8xx_wdt: Watchdog driver and macros cleanup

With the generic watchdog driver now implemented, this patch removes
some legacy stuff from the MPC8xx watchdog driver and its Kconfig
integration. CONFIG_MPC8xx_WATCHDOG is completely removed and
hw_watchdog_reset() is made static, as the watchdog will now get
serviced via the DM infrastructure if enabled via CONFIG_WATCHDOG.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
index d901240..40b2f4b 100644
--- a/drivers/watchdog/Makefile
+++ b/drivers/watchdog/Makefile
@@ -24,6 +24,6 @@
 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
+obj-$(CONFIG_WDT_MPC8xx) += mpc8xx_wdt.o
 obj-$(CONFIG_WDT_MT7621) += mt7621_wdt.o
 obj-$(CONFIG_WDT_MTK) += mtk_wdt.o