Relax the language around parallel_restorecon.

For boot time purposes, this is done in parallel across a set of child processes. `ueventd.cpp` in

this directory contains documentation on how the parallelization is done.

There is an option to parallelize the restorecon function during cold boot as well. This should only

be done for devices that do not use genfscon, which is the recommended method for labeling sysfs

nodes. To enable this option, use the below line in a ueventd.rc script:

There is an option to parallelize the restorecon function during cold boot as well. It is

recommended that devices use genfscon for labeling sysfs nodes. However, some devices may benefit

from enabling the parallelization option:

    parallel_restorecon enabled