roofs_*.bbclass: fix missing vardeps for do_rootfs

roofs_*.bbclass: fix missing vardeps for do_rootfs

As per lib/oe/rootfs.py and lib/oe/package_manager/???/__init__.py
the PACKAGE_FEED baseurl is defined as the joined paths of:
URIS/BASE_PATHS/ARCHS

Therefore, the do_rootfs task should depend furthermore on
PACKAGE_FEED_{BASE_PATHS,ARCHS} to properly retrigger a build if
the value changes.

Signed-off-by: Loic Domaigne (ljd) <tech@domaigne.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>