[bootlin/training-materials] 49194a: yocto: slides: update to using SPDX for LICENSE

[Luca Ceresoli]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: 49194a00751b5e6903e880371c0e78a60e29303e
      https://github.com/bootlin/training-materials/commit/49194a00751b5e6903e880371c0e78a60e29303e
  Author: Luca Ceresoli <luca.ceresoli at bootlin.com>
  Date:   2022-07-15 (Fri, 15 Jul 2022)

  Changed paths:
    M slides/yocto-licensing/yocto-licensing.tex
    M slides/yocto-recipe-advanced/yocto-recipe-advanced.tex
    M slides/yocto-recipe-basics/yocto-recipe-basics.tex

  Log Message:
  -----------
  yocto: slides: update to using SPDX for LICENSE

Yocto is migrating to SPDX identifiers and kirkstone warns out when using
old identifiers. Document that and update our examples.

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>