usb: phy: Add AM335x PHY driver

This driver is a redo of my earlier attempt. It uses parts of the
generic PHY driver and uses the new control driver for the register
the phy needs to power on/off the phy. It also enables easy access for
the wakeup register which is not yet implemented.
The difference between the omap attempt is:
- no static holding variable
- one global visible function which exports a struct with callbacks to
  access the "control" registers.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/phy/am35x-phy-control.h

@@ -0,0 +1,21 @@
+#ifndef _AM335x_PHY_CONTROL_H_
+#define _AM335x_PHY_CONTROL_H_
+
+struct phy_control {
+	void (*phy_power)(struct phy_control *phy_ctrl, u32 id, bool on);
+	void (*phy_wkup)(struct phy_control *phy_ctrl, u32 id, bool on);
+};
+
+static inline void phy_ctrl_power(struct phy_control *phy_ctrl, u32 id, bool on)
+{
+	phy_ctrl->phy_power(phy_ctrl, id, on);
+}
+
+static inline void phy_ctrl_wkup(struct phy_control *phy_ctrl, u32 id, bool on)
+{
+	phy_ctrl->phy_wkup(phy_ctrl, id, on);
+}
+
+struct phy_control *am335x_get_phy_control(struct device *dev);
+
+#endif