bitbake.conf/abi_version.conf: Update to use BasicHash signature generator

bitbake.conf/abi_version.conf: Update to use BasicHash signature generator

This switches to use the hash based signature generatior and update
layout_abi to match stamp file layout changes.

Angstrom and Poky did this a while ago. This brings the OE-Core defaults
into line with what is the best common practise at this point. Its been
discussed on the mailing lists and by the TSC at length, this just completes
the transition.

(From OE-Core rev: 4199efed48005a62267fa3374c33b13627d85f44)

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