[bootlin/training-materials] 5eafa7: yocto: slides: extend Varflags section

[Luca Ceresoli]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: 5eafa7db61af0d1e36c3bcea9038663e2f367291
      https://github.com/bootlin/training-materials/commit/5eafa7db61af0d1e36c3bcea9038663e2f367291
  Author: Luca Ceresoli <luca.ceresoli at bootlin.com>
  Date:   2023-03-10 (Fri, 10 Mar 2023)

  Changed paths:
    M slides/yocto-recipe-extra/yocto-recipe-extra.tex

  Log Message:
  -----------
  yocto: slides: extend Varflags section

Split in two slides and add:

 * Link to bitbake docs
 * mention that more varflags can be added freely
 * add [depends]
 * cleanup the examples with one bullet + one example per item

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