configs/lego_ev3_defconfig: enable brickd by default

This enables the brickd package by default on LEGO MINDSTORM EV3. This
program is important because it shuts down the system on low battery.
Without this, rechargeable batteries could be damaged.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>