rockchip: Enable building a SPI ROM image on jerry

Add a simple binman config and enable CONFIG_HAS_ROM so that U-Boot
produces a ROM for jerry.

Change the binman image definition to support multiple images, since it
may be used to build both u-boot-rockchip.bin and u-boot.rom

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/dts/rockchip-u-boot.dtsi b/arch/arm/dts/rockchip-u-boot.dtsi
index a2559e2..0451db7 100644
--- a/arch/arm/dts/rockchip-u-boot.dtsi
+++ b/arch/arm/dts/rockchip-u-boot.dtsi
@@ -6,7 +6,13 @@
 #include <config.h>
 
 / {
-	binman {
+	binman: binman {
+		multiple-images;
+	};
+};
+
+&binman {
+	simple-bin {
 		filename = "u-boot-rockchip.bin";
 		pad-byte = <0xff>;