msm: vidc: Limit the max secure instances to 2

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: Ia0d2d7eee1319c46dd67e404ca3a9b4854f11014
Signed-off-by: Manikanta Kanamarlapudi <kmanikan@codeaurora.org>