conf: add bblayers.conf.sample
conf: add bblayers.conf.sample

So if $BUILDDIR/conf/bblayers.conf doesn't exist, it automatically
gets created from this samplefile like in other OE distros.

Signed-off-by: Ioan-Adrian Ratiu <7ec73abcfe099fc5574c01312b62768070c80980@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt