Make function for managing speak_data_s

Make function for managing speak_data_s

In previous code, instance of speak_data_s created by ttsd_server.c but destroyed by ttsd_data.c.
This way of memory management is dangerous because invalid memory access can occur by the mistake
of developers.

This patch provides two new function for creating and destroying instance of speak_data_s.
These functions provide safe creation and destruction of the instance.

Change-Id: I016720eccbffd16bdfcb23878573caa1cb9f3115
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>