usb: typec: Provide definitions for the USB modes

Defining the USB modes from the latest USB Power Delivery
Specification - USB 2.0, USB 3.2 and USB4 - as special modal
states just like the Accessory Modes.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20191230142611.24921-14-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/usb/typec_altmode.h

@@ -101,6 +101,22 @@ enum {
 	TYPEC_MODE_DEBUG,			/* Debug Accessory */
 };
 
+/*
+ * USB4 also requires that the pins on the connector are repurposed, just like
+ * Alternate Modes. USB4 mode is however not entered with the Enter Mode Command
+ * like the Alternate Modes are, but instead with a special Enter_USB Message.
+ * The Enter_USB Message can also be used for setting to connector to operate in
+ * USB 3.2 or in USB 2.0 mode instead of USB4.
+ *
+ * The Enter_USB specific "USB Modes" are also supplied here as special modal
+ * state values, just like the Accessory Modes.
+ */
+enum {
+	TYPEC_MODE_USB2 = TYPEC_MODE_DEBUG,	/* USB 2.0 mode */
+	TYPEC_MODE_USB3,			/* USB 3.2 mode */
+	TYPEC_MODE_USB4				/* USB4 mode */
+};
+
 #define TYPEC_MODAL_STATE(_state_)	((_state_) + TYPEC_STATE_MODAL)
 
 struct typec_altmode *typec_altmode_get_plug(struct typec_altmode *altmode,