package/matchbox: remove superfluous conditional includes

Now that the matchbox package no longer forcibly add entries to the
PACKAGES list, and entirely relies on having proper packages, we can
safely include all matchbox sub-packages .mk files, and the pkg-infra
will take care of building only those that are enabled.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>