OMAP3+: VP: cleanup: move VP instance into voltdm, misc. renames

- move VP instance struct from vdd_info into struct voltage domain
- remove _data suffix from structure name
- rename vp_ prefix from vp_common field: accesses are now vp->common
- move vp_enabled bool from vdd_info into VP instance
- remove remaining references to omap_vdd_info

No functional changes.

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