omap: voltage: add a stub header file for external/regulator use

Needed as some of the voltage layer functionality is accessed from the
SMPS regulator driver.
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>

arch/arm/plat-omap/include/plat/voltage.h

+/*
+ * OMAP Voltage Management Routines
+ *
+ * Copyright (C) 2011, Texas Instruments, Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __ARCH_ARM_OMAP_VOLTAGE_H
+#define __ARCH_ARM_OMAP_VOLTAGE_H
+
+struct voltagedomain;
+
+struct voltagedomain *voltdm_lookup(const char *name);
+int voltdm_scale(struct voltagedomain *voltdm, unsigned long target_volt);
+unsigned long voltdm_get_voltage(struct voltagedomain *voltdm);
+
+#endif