Label /dev/ttyGF* as serial_device

In goldfish kernel 3.10, the goldfish_tty device instantiates virtual
serial ports as /dev/ttyGF* (e.g. /dev/ttyGF0), not as /dev/ttyS* as in
goldfish kernel 3.4. However, in the emulator's SELinux security policy,
there is no specific security context assigned to /dev/ttyGF*, and the
one inherited from /dev (u:object_r:device:s0) prevents services such as
qemud and goldfish-logcat from reading and writing ttyGF*. Consequently,
qemud terminates abnormally on the classic x86_64 emulator:

 init: Service 'qemud' (pid XXX) exited with status 1

Fix this issue by assigning /dev/ttyGF* the same security context as
/dev/ttyS*.

Change-Id: Ia7394dc217bd82f566c4d1b7eda3cc8ce3ac612f
Signed-off-by: Yu Ning <yu.ning@intel.com>