ARC: make a copy of flat DT

The flat DT (currently embedded in vmlinux) is in .init section.
The unflattened/binary tree doesn't copy strings through and references
them from orig flat DT - which could cause catestrohpy if of_* APIs are
called post init, say from a driver which is a loadable module.
Reported-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/mach_desc.h

@@ -82,4 +82,6 @@ __attribute__((__section__(".arch.info.init"))) = {	\
 };
 
 extern struct machine_desc *setup_machine_fdt(void *dt);
+extern void __init copy_devtree(void);
+
 #endif

arch/arc/kernel/devtree.c

@@ -106,3 +106,18 @@ struct machine_desc * __init setup_machine_fdt(void *dt)
 
 	return mdesc_best;
 }
+
+/*
+ * Copy the flattened DT out of .init since unflattening doesn't copy strings
+ * and the normal DT APIs refs them from orig flat DT
+ */
+void __init copy_devtree(void)
+{
+	void *alloc = early_init_dt_alloc_memory_arch(
+			be32_to_cpu(initial_boot_params->totalsize), 64);
+	if (alloc) {
+		memcpy(alloc, initial_boot_params,
+				be32_to_cpu(initial_boot_params->totalsize));
+		initial_boot_params = alloc;
+	}
+}

arch/arc/kernel/setup.c

@@ -354,6 +354,8 @@ void __init setup_arch(char **cmdline_p)
 
 	setup_arch_memory();
 
+	/* copy flat DT out of .init and then unflatten it */
+	copy_devtree();
 	unflatten_device_tree();
 
 	/* Can be issue if someone passes cmd line arg "ro"