lib.sh: new function mk() to handle trees in bulk

single-tree projects cannot be handled in bulk, e.g.
./mk -f project1 project2 project3

that is still the case, from the shell, but internally
it is now possible:
mk -f project1 project2 project3

mk() is a function that simply handles the given flag,
and all projects specified.

it does not handle cases without argument, for example
you cannot do:
mk -f

arguments must be provided. it can be used internally,
to simplify cases where multiple single-tree projects
must be handled, but *also* allows multi-tree projects
to be specified, without being able to actually handle
trees within that multi-tree project; so for example,
you can only specify coreboot, and then it would run
on every coreboot tree.

Signed-off-by: Leah Rowe <leah@libreboot.org>

script/trees

@@ -36,9 +36,7 @@ main()
 		project="${OPTARG#src/}"; shift 2
 	done
 	[ -z "$_f" ] && $err "missing flag (-m/-u/-b/-c/-x/-f/-s/-l/-n)"
-	[ -z "$project" ] && for p in $(ls -1 config/git); do
-		./mk $_f "$p" || $err "!./mk $_f $p"; :
-	done && return 1
+	[ -z "$project" ] && mk $_f $(ls -1 config/git) && return 1
 
 	[ -f "config/git/$project/pkg.cfg" ] || $err "'$project' not defined"