clk: msm: clock-cpu-8939: Add support for single cluster target

Currently clock-cpu-8939 code expects the target should have both
big and little clusters. Add additional checks to the code to make it
compatible with targets(msmgold) having a single cluster with only single
cluster-1 PLL.

Change-Id: I5b68edd9a6c9ffdf11b3ac7f431fb59985715c42
Signed-off-by: Jaydeep Sen <jsen@codeaurora.org>