libiconv-full: add clause to Makefile to actually install iconv

At present, if you select the iconv utility it will be built but not
installed. This patch adds the clauses necessary to the Makefile to
actually install iconv.

Signed-off-by: Mike Brady <mikebrady@eircom.net>
Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34530 3c298f89-4303-0410-b956-a3cf2f4a3e73