msm: acpuclock-krait: Remove use of QSB as a CPU or L2 clock source

QSB's rate is tied to the Apps fabric (or BIMC on 8974), which means
that its rate is unpredictable. When the CPU is running at a low
voltage, if the QSB clock source is selected, it's possible that the
CPU clock rate could increase beyond the safe limit for that voltage.

Instead of selecting QSB for power-collapse and hotplug scenarios,
select an always-on source with a predictable rate.

Change-Id: I7c39d443bf49371358d0a618693a6efe2f26fcc4
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>