SELinux labeling of filesystem files ignores symlinks. Unfortunately,
/vendor is a symlink on devices without vendor partition
(e.g., hikey). Thus, policy in directories which are used both for
devices with vendor partition and for devices without vendor partition
must be adjusted to match both /vendor and /system/vendor. It is
assumed that the /vendor symlink, if it exists at all, always points
to /system/vendor.

The alternative solution of adjusting vendor policy file labelling
rules at vendor policy build time, when the actual on-device paths are
known, was considered to make it harder to see how files are labelled
by looking solely at the source tree.

Test: Files under /vendor/bin/hw correctly labelled on sailfish,
      angler, and a device which uses the /vendor symlink.
Bug: 35431549
Change-Id: If6ccb2c9cb85b0589db03ab86de8071e15d5366f