package/{mesa3d, mesa3d-headers}: bump version to 21.1.5

package/{mesa3d, mesa3d-headers}: bump version to 21.1.5

Switch site to https://archive.mesa3d.org

Release notes:
- 21.1.2
  https://lists.freedesktop.org/archives/mesa-announce/2021-June/000632.html
- 21.1.3
  https://lists.freedesktop.org/archives/mesa-announce/2021-June/000633.html
- 21.1.4
  https://lists.freedesktop.org/archives/mesa-announce/2021-June/000635.html
- 21.1.5
  https://lists.freedesktop.org/archives/mesa-announce/2021-July/000637.html

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>