PPC: OF: Make sure kernel args match the U-Boot one

Since both platforms can boot the same kernel we must accept either
arg, so we make sure they are identical for now.

TODO: use a union or KMessage maybe?

headers/private/kernel/boot/platform/openfirmware/platform_kernel_args.h

@@ -19,6 +19,12 @@
 typedef struct {
 	void	*openfirmware_entry;
 	char	rtc_path[128];
+
+	// XXX: HACK: must match the U-Boot platform args
+	// FIXME: use a union instead?
+
+	// Flattened Device Tree blob
+	void	*fdt;
 } platform_kernel_args;
 
 #endif	/* KERNEL_BOOT_PLATFORM_OPENFIRMWARE_KERNEL_ARGS_H */