busybox: add fbset to default configs

Some drivers (like ti-gfx) need fbset and we can't select it when we
use BusyBox because it is provided by BusyBox and as a package.

Signed-off-by: Hadrien Boutteville <hadrien.boutteville@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: "Spenser Gilliland" <spenser@gillilanding.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>