watchdog: mpc8xxx: Add support for mpc83xx

Introduce a new compatible "fsl,pq2pro-wdt"
On mpc83xx, the prescaling factor is 0x10000.

Don't write the watchdog configuration register in
start.S as it can be written only once.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
diff --git a/arch/powerpc/cpu/mpc83xx/cpu.c b/arch/powerpc/cpu/mpc83xx/cpu.c
index a6c0635..f6ffe29 100644
--- a/arch/powerpc/cpu/mpc83xx/cpu.c
+++ b/arch/powerpc/cpu/mpc83xx/cpu.c
@@ -165,7 +165,7 @@
 }
 #endif
 
-#if defined(CONFIG_WATCHDOG)
+#if defined(CONFIG_WATCHDOG) && !defined(CONFIG_WDT)
 void watchdog_reset (void)
 {
 	int re_enable = disable_interrupts();