combo-layer: avoid too long command lines in update with history
As suspected, invoking "git archive" with all intended files as
parameters can run into command line length limitations. Splitting up
the parameters into multiple invocations (xargs-style) works and was
tested after encountering the situation in practice.
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
