buildhistory: enable committing history by default

buildhistory: enable committing history by default

The most common usage for buildhistory is with commits enabled so that
you actually collect history, rather than just keeping a snapshot of the
most recent build state, therefore default BUILDHISTORY_COMMIT to "1".
This really ought to have been the default in the beginning, I can't
really explain why it wasn't.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>