PM / AVS: SmartReflex: use omap_sr * for minmax interfaces

SmartReflex driver interface is natively divided to two parts:

- external SmartReflex interface
- interface between SmartReflex driver and SmartReflex Class

Functions which belong to AVS class interface can use
struct omap_sr* instead of struct voltatedomain*, to provide a
direct connection between SR driver and SR class. This allows
us to optimize and not do additional lookups where none is
required.

sr_configure_minmax() is interface function between SR driver
and SR class. It is typically used by Class driver to
configure MINMAXAVG module inside SmartReflex module.
Now it takes struct omap_sr* as input parameter.

Signed-off-by: Andrii Tseglytskyi <andrii.tseglytskyi@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>