classes/packagegroup: fix dbg/dev/ptest complementary packages
OE-Core commit
8981ed20234c42dc1f5cdef802ebe7214bd55238 (from 2013)
caused a regression where -dbg/-dev/-ptest packages weren't generated
for packagegroups because we weren't setting ALLOW_EMPTY for them.
Break out the code for adding complementary groups to its own
conditional so we can set ALLOW_EMPTY at the same time.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
