Turns out you can specify this using the PACKAGE_CLASSES
variable but you better not list it first.
(From yocto-docs rev: 9b160b15b3508e360fd57ac4375867d58cdc9709)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>