Makefile, skeleton: move the host skeleton logic to host-skeleton package

Makefile, skeleton: move the host skeleton logic to host-skeleton package

As part of the per-package SDK work, we want to avoid having logic
that installs files to the global HOST_DIR, and instead do it inside
packages. One thing that gets installed to the global HOST_DIR is the
minimal "skeleton" that we create in host:

 - the "usr" symbolic link for backward compatibility

 - the "lib" directory, and its lib64 or lib32 symbolic links

This commit moves this logic to a new host-skeleton package, and makes
all packages (except itself) depend on it.

While at it, use $(Q) instead of @ in the HOST_SKELETON_INSTALL_CMDS.

[Peter: drop host-patchelf reference in commit message]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>