siggen.py: Pass the datacache to signature generator classes

siggen.py: Pass the datacache to signature generator classes

The dataCache exposes much useful information to the singature generation code
for example its possible to figure out whether kernel dependencies are
important or not based on the RRECOMMENDS values.

We therefore pass this information to the handler and trust it to handle
any API changes in the dataCache structure.

For backwards compatibility, OE-Core is already updated to handle
the extra argument when it appears.

(Bitbake rev: 4ebc25155d5f96a7f63de22b52b18d045eb4dec7)

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