cdrkit only install genisoimage by default,but most tools use
mkisofs to generate an ISO9660/JOLIET/HFS hybrid filesystem,
so add a link to genisoimage with the name mkisofs to support
these tools.
Signed-off-by: Jibin Xu <jibin.xu@windriver.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>