mpc8xxx: fix DDR init value to use CONFIG_MEM_INIT_VALUE

Configuring custom memory init value using CONFIG_MEM_INIT_VALUE in
the board config file doesn't work and memory is always initialized
to the value 0xdeadbeef. Only use this default value if a board doesn't
define CONFIG_MEM_INIT_VALUE.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Andy Fleming <afleming@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>

arch/powerpc/cpu/mpc8xxx/ddr/ctrl_regs.c

@@ -1190,7 +1190,11 @@ static void set_ddr_data_init(fsl_ddr_cfg_regs_t *ddr)
 {
 	unsigned int init_value;	/* Initialization value */
 
+#ifdef CONFIG_MEM_INIT_VALUE
+	init_value = CONFIG_MEM_INIT_VALUE;
+#else
 	init_value = 0xDEADBEEF;
+#endif
 	ddr->ddr_data_init = init_value;
 }