buildroot

package: use SPDX short identifier for LGPLv3/LGPLv3+

We want to use SPDX identifier for license string as much as possible.
SPDX short identifier for LGPLv3/LGPLv3+ is LGPL-3.0/LGPL-3.0+.

This change is done using following command.
find . -name "*.mk" | xargs sed -ri '/LICENSE( )?[\+:]?=/s/LGPLv3(\+)?/LGPL-3.0\1/g'

Signed-off-by: Rahul Bedarkar <rahulbedarkar89@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>