fdt_support: Fix buffer overflow in fdt_fixup_memory_banks

When fdt_fixup_memory_banks is called with 2-cell address and size
fields in the device-tree (IE: 64-bit address and size), then it will
overflow its on-stack "tmp" buffer.

This fixes the buffer size and adds a comment explaining how many bytes
need to be allocated per record.

Signed-off-by: Kyle Moffett <Kyle.D.Moffett@boeing.com>
Cc: Jerry Van Baren <vanbaren@cideas.com>
Acked-by: Gerald Van Baren <vanbaren@cideas.com>

common/fdt_support.c

@@ -394,7 +394,7 @@ int fdt_fixup_memory_banks(void *blob, u64 start[], u64 size[], int banks)
 {
 	int err, nodeoffset;
 	int addr_cell_len, size_cell_len, len;
-	u8 tmp[banks * 8];
+	u8 tmp[banks * 16]; /* Up to 64-bit address + 64-bit size */
 	int bank;
 
 	err = fdt_check_header(blob);