msm: acpuclock-krait: Add voltage boost mode

Add support to bump up or down the voltage via sysfs.

 # echo 1 > /sys/module/acpuclock_krait/parameters/boost

enables the boost and

 # echo 0 > /sys/module/acpuclock_krait/parameters/boost

disables the boost. Boost mode is enabled by default for fast and
nominal devices because those devices could be at the boundaries
of the characterization thresholds and exhibit CPU/L1 errors.

Change-Id: If0dd4ed949188debbb55f82f07004b57548164f6
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>