machine/usb: refactoring descriptors into subpackage for modularity

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/usb/descriptor/classspecific.go

@@ -0,0 +1,17 @@
+package descriptor
+
+const (
+	classSpecificTypeLen = 5
+)
+
+type ClassSpecificType struct {
+	data []byte
+}
+
+func (d ClassSpecificType) Bytes() []byte {
+	return d.data[:d.data[0]]
+}
+
+func (d ClassSpecificType) Length(v uint8) {
+	d.data[0] = byte(v)
+}