of: consolidate definition of early_init_dt_alloc_memory_arch()

Most architectures use the same implementation. Collapse the common ones
into a single weak function that can be overridden.

Signed-off-by: Grant Likely <grant.likely@linaro.org>

drivers/of/fdt.c

@@ -11,6 +11,7 @@
 
 #include <linux/kernel.h>
 #include <linux/initrd.h>
+#include <linux/memblock.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/of_fdt.h>
@@ -700,6 +701,17 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname,
 	return 1;
 }
 
+#ifdef CONFIG_HAVE_MEMBLOCK
+/*
+ * called from unflatten_device_tree() to bootstrap devicetree itself
+ * Architectures can override this definition if memblock isn't used
+ */
+void * __init __weak early_init_dt_alloc_memory_arch(u64 size, u64 align)
+{
+	return __va(memblock_alloc(size, align));
+}
+#endif
+
 /**
  * unflatten_device_tree - create tree of device_nodes from flat blob
  *