serial: use property service to set ro.serialno

* SELinux is not happy with us modifying default.prop, and who
  can blame it? We shouldn't be writing to a file on / anyway.

* Utilize property service to set the prop instead.

Change-Id: I121ae8e21f8da5b7c825c6ad3ac53c26b5e4cdd3
set TARGET_NO_ADAPTIVE_PLAYBACK