syslinux: install helper programs to the host

Even though syslinux is built for the target, it does create helper
programs intended to be run on the host such as syslinux and extlinux.
This change installs these helper programs to the host so that they may be
called by post image creation scripts.

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>