U-Boot: HACK: Fix linking the kernel

* For now let's include the same fields in platform_kernel_args
than in the OF version.
* This allows linking the kernel.
Later on we should allow supporting more than a single boot platform,
to have a single kernel per arch.

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

@@ -17,6 +17,12 @@
 
 
 typedef struct {
+	// XXX: HACK: must match the OF platform args
+	// FIXME: use a union instead?
+	void	*openfirmware_entry;
+	char	rtc_path[128];
+
+	// TODO: add FDT
 	char dummy;
 } platform_kernel_args;