Using += makes it difficult to remove. Soft-set with ?= instead.
(From OE-Core rev: df850ff9e101afcc9983f907570abaf17421ba0f)
Signed-off-by: California Sullivan <california.l.sullivan@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>