hal: Update keep_alive to support silence playback on non-hdmi devices

Keep_alive can now handle silence playback on multiple concurrent
devices such as primary output devices as well as HDMI

Change-Id: I08cbec51394d23255e1a61928e0b2cad552b2ac0
Signed-off-by: Md Mansoor Ahmed <mansoor@codeaurora.org>
9 files changed