autofs: fix QA error when building without systemd

Building without systemd enabled results in:

WARNING: QA Issue: autofs: Files/directories were installed but not shipped
  /lib
  /lib/systemd
  /lib/systemd/system
  /lib/systemd/system/autofs.service

fix that in the PKGCONFIG way.

Signed-off-by: Joe MacDonald <joe.macdonald@windriver.com>