MidiService: limit number of devices

Also limit number of listeners and connections.

Bug: 210864154
Test: see bug for repro steps
Test: Check status with:  adb shell dumpsys midi
Test: Test: atest CtsMidiTestCases
Test: https://source.android.com/devices/audio/midi_test.html
Change-Id: If5ab4518873f52136f52d8ac654b78a72717838a