libz160: fix dependencies

libz160 is provided as binary. We need EABI toolchain with glibc to use
it.

[Thomas: adjust dependency comment according to Yann suggestions.]

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>