combo-layer: support updating up to arbitrary commit
Support defining the top commit up to which to update. In other words,
this makes it possible to update up to certain point other than the
branch head. The update point (git commitish) is given on the command
line by appending the component name(s) with a colon and the commitish,
e.g.
$ combo-layer update my_component:sha1
Only the "update" action supports this.
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
