msm: pm-8x60: Remove msm_pm_wait_cpu_shutdown()/verify_cpu_pc() APIs

The APIs are currently unused. They were added for the benefit of
the acpuclock-8960 driver, which needed them to ensure that CPUs
were really power-collapsed before their clocks were disabled.

The current acpuclock-krait driver solves this problem a different
way, by taking advantage of hardware features that were not
available in early (unreleased) versions of the Krait cores. Now,
instead of disabling the CPUs' clocks, a low-frequency always-on
clock source is selected and hardware clock gating is employed to
save power. With this, it is no longer necessary to wait for the
SPM to confirm the CPU has power-collapsed before acpuclock's
CPU_DEAD callback executed.

Change-Id: If93efea7c0bd4bb2943e1a1782217943eacf31a0
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>