tools/buildroot_config: Sync rootfs to devlib busybox & add '-o nice' to ps

Set CONFIG_MODPROBE_SMALL=n and CONFIG_STATIC=y to allign the busybox
binary of the rootfs with that of devlib (refer to
$LISA/tools/recipes/busybox.recipe).

Set CONFIG_MODPROBE_SMALL=n to avoid an issue with insmod related to its
return value.

Moreover, set CONFIG_FEATURE_PS_ADDITIONAL_COLUMNS=y so that /bin/ps
supports the '-o nice' specifier. This is needed to evaluate issues
related to lisa-test during load related PELT Invariance tests on the
target they happen. Load depens on task priority, i.e. task nice value.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>