classes/rootfs_rpm: improve speed of RPM rootfs construction

classes/rootfs_rpm: improve speed of RPM rootfs construction

Improve the performance of the RPM backend during do_rootfs by
performing most of the package name to file resolution in a separate
utility written in C, processing the entire list of packages at once
rather than running rpm on the command line which loads the RPM database
for every package.

(From OE-Core rev: 9135d351ba7cb21e50239d2b310565680bd4fdca)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>