package/dbus-cpp: switch to libefl

The libecore package will be removed in a followup
patch, so switch to libefl package which contain an
updated version of libecore.

Reported-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>