ARM/u-boot: Add support for FDTs passed in the uImage

Since we're using multi-part uImage format, we can add the FDT as
a seperate "blob" in the uImage, if the used U-Boot version is not
"FDT enabled".

This is used for example for our Verdex target. Currently I've got
a local hack in the platform/u-boot/Jamfile, looking into pulling
in the FDT files and a proper Jam setup to do that properly...

headers/private/kernel/boot/platform/u-boot/platform_stage2_args.h

@@ -12,6 +12,8 @@
 struct platform_stage2_args {
 	void *boot_tgz_data;
 	uint32 boot_tgz_size;
+	void *fdt_data;
+	uint32 fdt_size;
 };
 
 #endif	/* KERNEL_BOOT_PLATFORM_UBOOT_STAGE2_H */