msm: acpuclock-krait: Add a debugfs interface

Add a debugfs interface to peek at acpuclock driver state. Also
include support for enabled and disabling CPU and L2 hardware
clock gating, which is sometimes useful when performing clock
measurements.

Change-Id: Ia80b8f0b0ef85280ea93d145a049cdab15d4116e
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>