msm: mdss: hdmi: fix no audio over HDMI on device bootup

In case of HDMI interface as primary, if device boots up with
HDMI connected, external interface driver is unable to notify
audio events as audio codec is getting registered later.
Add change to send audio event once audio codec gets registered.

Change-Id: I8d630adf892714ff2eb4d6039dc058b54c425b83
Signed-off-by: Narender Ankam <nankam@codeaurora.org>