msm: acpuclock-8960: Support booting with fewer CPUs

Allow booting with only a subset of the CPUs enabled by default. The
others can potentially be added later with hotplug, at which point
the voltage, bus and clock requests for them will be applied.

Change-Id: If57eb1d2e13071474696bfdcc77842da289f9a0e
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>