Split do_packagedata task from do_package

Split do_packagedata task from do_package

Currently, do_rootfs has a dependency on all the do_package output being present
due to its usage of the pkgdata directories. This means that if you run:

bitbake xxxx-image -c rootfs

you end up having to fetch and unpack all the do_package data which is usually
large and inefficient. It also means rm_work has to leave all the do_package
data lying around so rootfs works.

This patch splits the actual creation of the pkgdata directory off into a separate
task, "packagedata" which happens immediately after do_package. We can then remap
the dependencies so this task is depended upon, not do_package. Sstate can then be
programmed not to require do_package at the appropriate times.

Whilst this patch doesn't do so, it opens the possibility of rm_work wiping
out the do_package output from WORKDIR as long as it also removed the do_package
stamp (both normal and setscene variants) and allowing more space savings
with rm_work which has been regularly requested.

(From OE-Core rev: 6107ee294afde395e39d084c33e8e94013c625a9)

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