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/arch/powerpc/cpu/mpc8xx/Kconfig b/arch/powerpc/cpu/mpc8xx/Kconfig
index b0e90a0..3e8ea38 100644
--- a/arch/powerpc/cpu/mpc8xx/Kconfig
+++ b/arch/powerpc/cpu/mpc8xx/Kconfig
@@ -25,9 +25,9 @@
 
 endchoice
 
-config MPC8xx_WATCHDOG
-	bool "Watchdog"
-	select HW_WATCHDOG
+#config MPC8xx_WATCHDOG
+#	bool "Watchdog"
+#	select HW_WATCHDOG
 
 config 8xx_GCLK_FREQ
 	int "CPU GCLK Frequency"