gresource-tool has optional support for using libelf to extract resources from
ELF files, so add a PACKAGECONFIG in case someone wants this.
(From OE-Core rev: 93f08a036343d4df1aefe9793a7a9ab5b296f5b5)
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>