msm: vidc: Limit the max secure instances to 3

Limit the secure instances to 2 in platform data,
but as per the design driver allows 3rd instance
as well since the secure flags were updated later
for the current instance. Hence total no of
concurrent secure sessions support will be
max-secure-instances + 1.

Change-Id: Iaf91f321a40c590936babb703d58b06dd6eccc25
Signed-off-by: Prabhakar Reddy Krishnappa <prkrishn@codeaurora.org>