package.bbclass: Add data expansion to do_split_packages()

package.bbclass: Add data expansion to do_split_packages()

do_split_packages is often called with parameters which need expansion.
This happens to work at the moment since python functions are expanded
before execution but likely will not happen in future and isn't good
code practise.

Expand the common parameters do_split_packages() to avoid regressions.

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