package/scripts: Fix FILES_INFO handling

There is a long standing bug where FILES_INFO isn't written into pkgdata
with a package suffix. This means if the files are read into the datastore
as intended, the last one "wins".

Fix this to work as intended. Most of the call sites using the data need
to be updated to handle this and the overrides change correctly.

Also fix some other problematic references noticed along the way.

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