servo: doxygen comments and adding mfg to upm.h

Signed-off-by: John Van Drasek <john.r.van.drasek@intel.com>

src/servo/servo.h

@@ -45,6 +45,7 @@ namespace upm {
  * the maximum period.
  *
  * @defgroup servo libupm-servo
+ * @ingroup seeed emax pwm servos
  */
 class Servo {
     public:

src/upm.h

@@ -284,6 +284,12 @@
  * @ingroup byman
  */
 
+/**
+ * @brief EMax
+ * @defgroup emax EMax
+ * @ingroup byman
+ */
+
 /**
  * @brief EpicTinker
  * @defgroup epict EpicTinker