openwrt: less verbose during toolchain build

Printing everything during the toolchain build slows down the build
since it uses only a single core and also overloads Jenkins with a flood
of shell output. Since build logs are stored, speed things up.

Signed-off-by: Paul Spooren <mail@aparcar.org>
Signed-off-by: Holger Levsen <holger@layer-acht.org>