vexpress64: Enable OF_CONTROL and OF_BOARD for VExpress64

Capture x0 in lowlevel_init.S as potential fdt address. Modify
board_fdt_blob_setup to use fdt address from either vexpress_aemv8.h
or lowlevel_init.S.

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/board/armltd/vexpress64/Makefile b/board/armltd/vexpress64/Makefile
index 868dc4f..1878fbe 100644
--- a/board/armltd/vexpress64/Makefile
+++ b/board/armltd/vexpress64/Makefile
@@ -3,5 +3,5 @@
 # (C) Copyright 2000-2004
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-obj-y	:= vexpress64.o
+obj-y	:= vexpress64.o lowlevel_init.o
 obj-$(CONFIG_TARGET_VEXPRESS64_JUNO)	+= pcie.o