conf: cleanup in bblayers.conf.sample
conf: cleanup in bblayers.conf.sample

Small cleanup in bblayers.conf.sample. All layers are appended with '+='
now, because the layers poky/meta and poky/meta-yocto are not special.
The change makes the file layout more regular.

Signed-off-by: Stefan Christ <c04781dbce194802ec6a6311a1200fbcd0141e96@phytec.de>

PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec,PHYTEC-Messtechnik-GmbH/meta-phytec