sstate: Improve handling of machine specific manifests
Now do_package isn't machine specific, we're only left with do_populate_sysroot as a
machine specific task. This change marks only the machine specific manifests as machine
specific, defaulting to PACKAGE_ARCH for everything else.
This means we do less work where there are multiple machines using the same
core package architecture and we can start to clean up the sstate duplicate files
whitelist.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
