msm: smd_tty: use pm_qos for bt performance.

A2DP audio skips out every 8-10 seconds in idle.
cpuidle is working and sometime A2DP audio skips in that time.

Use pm_qos to avoid this problem.

Change-Id: I00701c89cb9d5723e17928f452696db21e107ab0
Signed-off-by: Iliyan Malchev <malchev@google.com>