AP_IOMCU: rename and make enum RC_Channel::ControlType

Type:: is too generic; get_type should probably be get_control_type

libraries/AP_IOMCU/AP_IOMCU.cpp

@@ -958,7 +958,7 @@ bool AP_IOMCU::setup_mixing(RCMapper *rcmap, int8_t override_chan,
         MIX_UPDATE(mixing.rc_reversed[i], c->get_reverse());
 
         // cope with reversible throttle
-        if (i == 2 && c->get_type() == RC_Channel::RC_CHANNEL_TYPE_ANGLE) {
+        if (i == 2 && c->get_type() == RC_Channel::ControlType::ANGLE) {
             MIX_UPDATE(mixing.throttle_is_angle, 1);
         } else {
             MIX_UPDATE(mixing.throttle_is_angle, 0);