buildroot

manual: update old references to support/scripts

There were still some references to the old location of the scripts in
the manual. Replace them by utils/.

While we're at it, remove the redundant ./ at the beginning of some of
the example commands.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>