core/pkg-generic: store file->package list for staging and host too

core/pkg-generic: store file->package list for staging and host too

Currently, we store the list of files installed in target/ and associate
each of them to the package that installed it.

However, we sometimes may need to know what package installed which file
in staging/, for example to debug header collision, or in host/, to
debug what package installed what host tool.

Enhance the step instrumentation to also generate the list for staging/
and host/.

We maintain backward compatibility, for external scripts that wanted to
parse the previously existing list, by not renaming the target-related
package list. Only the staging- and host-related lists are named after
staging and host.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: fix missing word in .mk comment.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>