rpm: Ensure compression parallelism isn't coded into rpms

We don't want the compression thread numbers to be encoded into the rpm
since this results in the rpm not being deterministic. Add a patch
from Alex Kanavin which addresses this issue (was queued for rpm 4.17
but we need to fix this with 4.16 too).

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>