OMAP3+: voltage domain: move PMIC struct from vdd_info into struct voltagedomain

Move structure containing PMIC configurable settings into struct
voltagedomain.  In the process, rename from omap_volt_pmic_info to
omap_voltdm_pmic (_info suffix is not helpful.)

No functional changes.

Signed-off-by: Kevin Hilman <khilman@ti.com>