package: use SPDX short identifier for MPL family licenses

package: use SPDX short identifier for MPL family licenses

We want to use SPDX identifier for license string as much as possible.
SPDX short identifier for MPLv1.0/MPLv1.1/MPLv2.0 is MPL-1.0/MPL-1.1/
MPL-2.0.

This change is done using following command.
find . -name "*.mk" | xargs sed -ri '/LICENSE( )?[\+:]?=/s/MPLv([1-2]\.[0-1])/MPL-\1/g'

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