msm: mdss: hdmi: proper state validation and buffer handling

Validate current hdcp lib state before starting new hdcp session.
Double buffer the sink message and protect its access with mutex
to handle fast re-authentication requests.

Change-Id: I039b1a0c818a2e66eef583afb15420ce8587a75c
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>