arm64: dts: Make sure that all DTBs are 64bit aligned

Start of DTB should be 64bit aligned that's why also make sure that end is
also 64bit aligned. It is not required but it is nice thing to do.
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/arm/dts/Makefile

@@ -1127,7 +1127,7 @@ dtb-$(CONFIG_TARGET_EA_LPC3250DEVKITV2) += lpc3250-ea3250.dtb
 targets += $(dtb-y)
 
 # Add any required device tree compiler flags here
-DTC_FLAGS +=
+DTC_FLAGS += -a 0x8
 
 PHONY += dtbs
 dtbs: $(addprefix $(obj)/, $(dtb-y))