msm-core: Retrieve voltage plan for only cpus listed cpumask

Currently, the implementation assumes that all the clusters have 4 cores
within it. This information overrides the data that is provided by the
userspace. Provide voltage plan update to only those cpus request by the
userspace in cpumask attribute.

Change-Id: I5be720f725919b831acd51591a80e14b2816f21d
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>