Refactor yumpkg5 arch handling

When I originally wrote the mutli-arch support in this module, it was
done hastily and was not well-designed. For instance, it assumes that
x86_64 is the only arch for which packages from other arches are
supported. It additionally doesn't support ARM architectures at all,
making it completely useless on those devices.

This commit handles architectures in a more elegant way. Salt will now
only refer to the package with the arch appended if the arch both A) is
not 'noarch', and B) does not match the 'osarch' grain. This cleans
up the logic significantly, as well as enabling proper support for ARM
devices (though this is still untested).