Modify EndpointInfo to provide meaningful data rather than raw USB

descriptor values. E.g. for the user, the distinction between
MaxIsoPkt and MaxPktSize is irrelevant, only the calculated max packet
size matters.

usb/config_test.go

@@ -9,20 +9,23 @@ func TestEndpointInfo(t *testing.T) {
 	}{
 		{
 			ep: EndpointInfo{
-				Address:       0x86,
-				Attributes:    0x02,
+				Number:        6,
+				Direction:     EndpointDirectionIn,
+				TransferType:  TransferTypeBulk,
 				MaxPacketSize: 512,
 			},
-			want: "Endpoint #6 IN  bulk - unsynchronized data [512 0]",
+			want: "Endpoint #6 IN (address 0x86) bulk [512 bytes]",
 		},
 		{
 			ep: EndpointInfo{
-				Address:       0x02,
-				Attributes:    0x05,
+				Number:        2,
+				Direction:     EndpointDirectionOut,
+				TransferType:  TransferTypeIsochronous,
 				MaxPacketSize: 512,
-				MaxIsoPacket:  512,
+				IsoSyncType:   IsoSyncTypeAsync,
+				UsageType:     IsoUsageTypeData,
 			},
-			want: "Endpoint #2 OUT isochronous - asynchronous data [512 512]",
+			want: "Endpoint #2 OUT (address 0x02) isochronous - asynchronous data [512 bytes]",
 		},
 	} {
 		if got := tc.ep.String(); got != tc.want {