layer.conf: Use .= for adding to BBPATH and += to BBFILES
layer.conf: Use .= for adding to BBPATH and += to BBFILES

Fixes parsing errors which is appearing after this commit to
meta-openembedded

http://cgit.openembedded.org/meta-openembedded/commit/?id=3c21a46020bd0816579648f684c41dbd6333583e

This triggers
exception NameError: name 'base_contains' is not defined
without this change

Signed-off-by: Andrei Gherzan <0401b4310c02ae595fc6a2b84ead073cab9b0442@windriver.com>
Signed-off-by: Christopher Larson <4c8c411260e601995081b113a5ef94a26eff2b25@mentor.com>
Signed-off-by: Joe MacDonald <75b725b40bc588a7079b9d1596fafc9f579dbd52@windriver.com>

sesamstrasse/meta-openembedded,sesamstrasse/meta-openembedded,sesamstrasse/meta-openembedded,sesamstrasse/meta-openembedded,sesamstrasse/meta-openembedded