arm64: zynqmp: Print multiboot reg in decimal

It is better to print multiboot value in decimal because boot images are
also composed in decimal not in hex.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

board/xilinx/zynqmp/zynqmp.c

@@ -354,7 +354,7 @@ static int multi_boot(void)
 
 	multiboot = readl(&csu_base->multi_boot);
 
-	printf("Multiboot:\t%x\n", multiboot);
+	printf("Multiboot:\t%d\n", multiboot);
 
 	return 0;
 }