package/bluez5_utils: enable support for external ell
Bluez5' support for the mesh profile needs ell, the Embedded Linux
Library, at least version 0.28.
Although Bluez5 bundles an internal copy of ell version 0.28, we prefer
building with external libraries.
Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>