USB: Add the USB 2.0 extension descriptor.

This device descriptor was added by the recent USB Link Power Management (LPM)
ECN.  It indicates whether the USB device supports LPM.

This descriptor is grouped under a Binary Device Object Store (BOS) descriptor.
Update the BOS comments to indicate any USB device (not just wireless USB
devices) can implement BOS descriptors.
Signed-off-by: NSarah Sharp <sarah.a.sharp@intel.com>
Acked-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

include/linux/usb/ch9.h

@@ -455,7 +455,7 @@ struct usb_encryption_descriptor {
 
 /*-------------------------------------------------------------------------*/
 
-/* USB_DT_BOS:  group of wireless capabilities */
+/* USB_DT_BOS:  group of device-level capabilities */
 struct usb_bos_descriptor {
 	__u8  bLength;
 	__u8  bDescriptorType;
@@ -501,6 +501,16 @@ struct usb_wireless_cap_descriptor {	/* Ultra Wide Band */
 	__u8  bReserved;
 } __attribute__((packed));
 
+#define	USB_CAP_TYPE_EXT		2
+
+struct usb_ext_cap_descriptor {		/* Link Power Management */
+	__u8  bLength;
+	__u8  bDescriptorType;
+	__u8  bDevCapabilityType;
+	__u8  bmAttributes;
+#define USB_LPM_SUPPORT			(1 << 1)	/* supports LPM */
+} __attribute__((packed));
+
 /*-------------------------------------------------------------------------*/
 
 /* USB_DT_WIRELESS_ENDPOINT_COMP:  companion descriptor associated with