ARM: OMAP: voltage: renamed vp_vddmin and vp_vddmax fields

These are now called vddmin and vddmax, as these fields will be used
globally for selecting voltage ranges for a pmic channel, and not
only for voltage processor.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>