drivers: qcom-cpufreq: Move disabling of clocks to CPU_DYING

Some SoCs contain CPU clock trees the elements of which are
gated off when the CPUs enter power collapse. This includes
sources of glitch free muxes; therefore when the CPUs enter
power collapse, those muxes cannot be switched.

Now in the cpufreq driver, the CPU clocks are disabled in
the CPU_DEAD notifier, which implies that the CPU muxes
are switched to a safe source *after* the CPUs are power
collapsed. However, the source of the GFMUX may already be
turned off, causing the mux to get stuck.

Ideally, the mux should allow a static switch, since the
clock to the CPU is gated. Some implementations do not
allow this.

Change-Id: I37d3426f20250c59756a0b55d1284efad5359a23
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>