msm: vidc: Make sku index an optional property

SKU index is not applicable for all targets. Hence no need
to keep it mandatory. SKU related changes will happen only
when the property is present otherwise will default to 0.

Change-Id: I88076ea95bccd4130202c055e5c148d817dd302e
Signed-off-by: Chinmay Sawarkar <chinmays@codeaurora.org>