We have cases where we'd like to inherit this class by default but allow
special cases to override it. This change makes the code of the class
conditional on PACKAGE_ARCH remaining set to "all", allowing it to be
overridden. packagegroup usage is one case this is desirable.
(From OE-Core rev: 7dd91402b719ac62b51088f234354f82bfa9c4b6)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>