rauc: select host-squashfs as a host dependency

The rauc host tool (used to generate update bundles) runs mksquashfs so
host-squashfs is required for it to work at runtime.

Signed-off-by: Andrey Yurovsky <yurovsky@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>