5xxx, fdt: move fdt_fixup_memory() to cpu.c file

u-boot updates, before starting Linux, the memory node in the
DTS. As this is a "standard" feature, move this functionality
to the cpu.c file for mpc5xxx and mpc512x processors.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/cpu/mpc5xxx/cpu.c b/cpu/mpc5xxx/cpu.c
index efa64c7..2a28df4 100644
--- a/cpu/mpc5xxx/cpu.c
+++ b/cpu/mpc5xxx/cpu.c
@@ -157,6 +157,7 @@
 	}
 
 #endif
+	fdt_fixup_memory(blob, (u64)bd->bi_memstart, (u64)bd->bi_memsize);
 }
 #endif