msm: acpuclock-krait: 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: Iff0758e6d3c79435c2c144da70079c8d60626224
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>