drivers: of: add definition of early_init_dt_alloc_reserved_memory_arch

The function early_init_dt_alloc_reserved_memory_arch is defined
in drivers/of/of_reserved_mem.c but is not declared in any of the
header files. Add the declaration of this to avoid the warning:

drivers/of/of_reserved_mem.c:31:19: warning: symbol 'early_init_dt_alloc_reserved_memory_arch' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
[robh: drop extern from declaration]
Signed-off-by: Rob Herring <robh@kernel.org>

include/linux/of_reserved_mem.h

@@ -31,6 +31,13 @@ typedef int (*reservedmem_of_init_fn)(struct reserved_mem *rmem);
 int of_reserved_mem_device_init(struct device *dev);
 void of_reserved_mem_device_release(struct device *dev);
 
+int early_init_dt_alloc_reserved_memory_arch(phys_addr_t size,
+					     phys_addr_t align,
+					     phys_addr_t start,
+					     phys_addr_t end,
+					     bool nomap,
+					     phys_addr_t *res_base);
+
 void fdt_init_reserved_mem(void);
 void fdt_reserved_mem_save_node(unsigned long node, const char *uname,
 			       phys_addr_t base, phys_addr_t size);