msm: lpm-levels: Support for cluster power management

Add power management support for multilevel cluster. The code is redesigned
to support low power modes with multiple hierarchies of clusters.

Change-Id: I0d0142e53bf2fe6152e7791f09bcb4d35a82e461
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>