mk: initfs: Restore explicit directory commands (follows up d29ffe5)
mk: initfs: Restore explicit directory commands (follows up d29ffe5)

The previous change has not been tested well enough. It introduced a
regression on Make >= 3.82, reproduced even on non-parallel builds.

The real solution of the issue is fixing double-slash paths, this is
already done in d29ffe5, in build-gen.mk.

Kakadu/embox,mike2390/embox,mike2390/embox,Kakadu/embox,Kakadu/embox,Kakadu/embox,mike2390/embox,embox/embox,embox/embox,embox/embox,Kakadu/embox,mike2390/embox,embox/embox,embox/embox,mike2390/embox,Kakadu/embox,embox/embox,Kakadu/embox,mike2390/embox,mike2390/embox