package_rpm/update-alternatives: fix package's provides

Currently we have:
  $ rpm -qp --provides tmp/deploy/rpm/core2_64/bash-5.1.8-r0.core2_64.rpm
  bash = 5.1.8-r0

This is incorrect as bash provides /bin/bash and /bin/sh. This is caused by
incomplete conversion of new override syntax, which breaks the per-file
parsing of package_rpm.

With this patch, we have:
  $ rpm -qp --provides tmp/deploy/rpm/core2_64/bash-5.1.8-r0.core2_64.rpm
  /bin/bash
  /bin/sh
  bash = 5.1.8-r0

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>