configs/beelink_gs1: use Python 3.x

Since the bump to U-Boot 2020.01 in commit
e210080d, it needs Python 3.x on the
host.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/535054357



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Acked-by: Clément Péron <peron.clem@gmail.com>
[yann.morin.1998@free.fr: update with the new NEEDS_PYTHON semantics]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>