libexternal: change action safe property to persist

It is more probable that end user always use same TV to connect.
Hence make the action safe property persist, so that it is
persistent across reboot
Also, change property to sys. from hw. so that hwc can write

Change-Id: I5a77156012d121e28d1adbadb9162fcdf7ca3edd
CRs-fixed: 472431
2 files changed