package_rpm.bbclass: use multithreaded xz compression
RPM's default is single-threaded gz; the change greatly helps with
both buildtimes (when there is a small number of large-sized packages)
and disk space taken by resulting rpms.
(From OE-Core rev:
f108c4d09926bd28e7a57b665fc8cb5373827780)
Signed-off-by: Alexander Kanavin <alexander.kanavin@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
