riscv: ae350: Switch to use binman to generate u-boot.itb

Use the new BINMAN_STANDALONE_FDT option for AE350 based SPL defconfigs,
so that binman is now used to generate u-boot.itb.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Rick Chen <rick@andestech.com>

arch/riscv/dts/ae350_32.dts

@@ -1,5 +1,7 @@
 /dts-v1/;
 
+#include "binman.dtsi"
+
 / {
 	#address-cells = <1>;
 	#size-cells = <1>;

arch/riscv/dts/ae350_64.dts

@@ -1,5 +1,7 @@
 /dts-v1/;
 
+#include "binman.dtsi"
+
 / {
 	#address-cells = <2>;
 	#size-cells = <2>;