ipkg: mark as deprecated

ipkg dates back to the early 2000s when Compaq started the handhelds.org
project, it hasn't seen development since 2006, got forked as opkg a decade
ago and is starting to cause autobuilder issues, so mark it as deprecated.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ipkg/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_IPKG
 	bool "ipkg"
+	depends on BR2_DEPRECATED_SINCE_2016_08
 	help
 	  The Itsy Package Installer from handhelds.org