Export the OPP functions for use by driver modules.

Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Kevin Hilman <khilman@ti.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

[nm@ti.com: expansion of functions exported]
Signed-off-by: NNishanth Menon <nm@ti.com>
Signed-off-by: NLiam Girdwood <lrg@ti.com>
Acked-by: NKevin Hilman <khilman@ti.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>