In some cases we need to check specifically for siginfo files, in
some cases we need to check for the actual sstate objects themselves.
Therefore make this a parameter to the function. A fallback to the
previous function style is maintained for now.
(Bitbake rev: 18d3a03e1b07c98b2dce46eb94f30de1a2b4320b)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>