SmartReflex: allow to disable SR calibrations

Based on steven676's work for encore.

[steven@steven676.net: add voltdm->name to log message]
encore: disable SmartReflex calibration for OPP5 when overclocking

It appears the SR class 1.5 calibration process itself is causing
problems for some users at the non-standard 1100/1200 MHz overclocks.
Disable the calibration process for OPP5, effectively locking the
voltage for that OPP to 1.375 V.
encore defconfigs: allow 1.2 GHz overclock

With any luck, the previous changes to disable SmartReflex at the
highest OPP should allow most people to hit 1.2 GHz stably.