support/dependencies: treat BSD-tar like the other cases

support/dependencies: treat BSD-tar like the other cases

Currently, when we detect that tar is BSD-tar, we fake an unsupported
version (major, minor) and rely on the version check to reject BSD-tar.

There is no reason to use such shenanigans, when we can simply reject it
from the onset.

Simplify the logic:
  - use positive logic in the condition
  - directly exit in error

Also, comment that case like the other cases are commented.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>