image: Rename load_addr, save_addr, save_size

These global variables are quite short and generic. In fact the same name
is more often used locally for struct members and function arguments.

Add a image_ prefix to make them easier to distinguish.

Signed-off-by: Simon Glass <sjg@chromium.org>

net/net.c

@@ -636,7 +636,7 @@ restart:
 				printf("Bytes transferred = %d (%x hex)\n",
 				       net_boot_file_size, net_boot_file_size);
 				env_set_hex("filesize", net_boot_file_size);
-				env_set_hex("fileaddr", load_addr);
+				env_set_hex("fileaddr", image_load_addr);
 			}
 			if (protocol != NETCONS)
 				eth_halt();