docs/manual: document MPL licenses

Many packages are provided under MPL v1.1 and v2.0. Document it under
License abbreviations section.

Cc: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Rahul Bedarkar <rahul.bedarkar@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/legal-notice.txt

@@ -151,6 +151,12 @@ Buildroot, with the name used in the manifest files:
 * `ISC`:
   https://opensource.org/licenses/ISC[
   ISC License];
+* `MPLv1.1`:
+  https://www.mozilla.org/en-US/MPL/1.1[
+  Mozilla Public License Version 1.1]
+* `MPLv2.0`:
+  https://www.mozilla.org/en-US/MPL/2.0[
+  Mozilla Public License Version 2.0]
 
 [[legal-info-buildroot]]
 === Complying with the Buildroot license