linux-firmware: add PE back

Add PE (package epoch) from the previous version of the recipe to avoid
problems with package upgrade due to changed versioning scheme.

See:
http://lists.openembedded.org/pipermail/openembedded-core/2019-August/285633.html



Signed-off-by: Oleksandr Kravchuk <open.source@oleksandr-kravchuk.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>