package: Add auto package splitting of .debug files
Creating FILES_${PN}-dbg is tedious and also pretty pointless. We might as well
assume ".debug" is a special directory name and split into -dbg automatically.
This change does so without changing the rest of the splitting logic too much.
It can be disabled for the cases where we really do want manual control of
the -dbg packages (e.g. qt4) with NOAUTOPACKAGEDEBUG = "1".
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
