mb/qemu-aarch64: Fix include path for device_tree.h

Recently merged commit 8cc1d79ed0 (mainboard/qemu-aarch64: Get top
of memory from device-tree blob) missed a rebase and hence needs the
include path updated.

Tested `make qemu` for qemu-aarch64.

Change-Id: Id669eeaabbc1710bb7e408659f2d79f682427919
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83945
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>

src/mainboard/emulation/qemu-aarch64/cbmem.c

@@ -3,7 +3,7 @@
 #include <cbmem.h>
 #include <ramdetect.h>
 #include <symbols.h>
-#include <device_tree.h>
+#include <commonlib/device_tree.h>
 
 DECLARE_REGION(fdt)
 uintptr_t cbmem_top_chipset(void)