smbios: Move smbios_write_type to the C file

This type is not used outside the smbios.c file so there is no need for it
to be in the header file. Move it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/lib/smbios.c b/lib/smbios.c
index 1e10fa8..b1171f5 100644
--- a/lib/smbios.c
+++ b/lib/smbios.c
@@ -18,6 +18,16 @@
 #endif
 
 /**
+ * Function prototype to write a specific type of SMBIOS structure
+ *
+ * @addr:	start address to write the structure
+ * @handle:	the structure's handle, a unique 16-bit number
+ * @node:	node containing the information to write (ofnode_null() if none)
+ * @return:	size of the structure
+ */
+typedef int (*smbios_write_type)(ulong *addr, int handle, ofnode node);
+
+/**
  * struct smbios_write_method - Information about a table-writing function
  *
  * @write: Function to call