mdss: msm: hdmi: use circular buffer for CEC rx

There's only one CEC message buffer which could be
overwritten if the next interrupt happens before
the workthread reads the buffer.

To resolve this, defined 4 circular buffers (practially
3 due to linux circular buffer limitation) to rotate
the buffer.

Since CEC is slow bus, 3 buffers should be enough
to avoid potential message overwriting.

Change-Id: I538c5902e95edb2231077c1c03a73f690ce68f1a
Signed-off-by: Venkata Prahlad Valluru <vvalluru@codeaurora.org>