msm: vidc: set multistream mode for worst case scratch buffer requirement

In case of secure mode, worst case scratch buffer requimrement is
calulated upfront to avoid any delay in reallocation during the
resolution change. Worst case buffer requirement will be calulated
for max resolution and multistream mode enabled. This commit will
enable multistream mode if required to get worst case buffer requirements.

Change-Id: Iaafed40218d8a79e07584c87172bdadb62276cc6
Signed-off-by: Deepak Kushwah <dkushwah@codeaurora.org>