busybox: add comments to separate Runit from SELinux content in defconfig

busybox: add comments to separate Runit from SELinux content in defconfig

There is no break in busybox's "defconfig" file to show where Runit
settings suddenly morph into SELinux settings, so add some comments.

(From OE-Core rev: 0fa590ed6c26aa065a9da8edbf65436fa1f6d04f)

(From OE-Core rev: 21c3d1b354dbb6cd6f3d574785f70858d828d977)

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>