feat: add MIDI 2.0 Device class driver (USB-MIDI 2.0)

Add native USB-MIDI 2.0 Device class driver to TinyUSB. Implements the
USB-MIDI 2.0 specification with both Alt Setting 0 (MIDI 1.0 fallback)
and Alt Setting 1 (UMP native) descriptor support.

Driver features:
- UMP (Universal MIDI Packet) read/write with atomic message framing
- Protocol negotiation: Endpoint Discovery, Config Request/Notify,
  Function Block Discovery (embedded in driver)
- Group Terminal Block descriptor via GET_DESCRIPTOR
- Alt Setting switch handler with endpoint re-arm
- Static allocation, no dynamic memory, ISR-safe

Build system:
- Register midi2d_* in usbd.c driver table
- Add TUD_MIDI2_DESCRIPTOR macros to usbd.h
- Add config defaults (CFG_TUD_MIDI2_*) to tusb_option.h
- Add midi2_ump_word_count() to midi.h (shared by Device and Host)
- Add midi2_device.c/h to family.cmake and CMakeLists.txt
- Add midi2_device.h include to tusb.h

All changes guarded by #if CFG_TUD_MIDI2 (default 0). Zero impact on
existing drivers and examples.

Tested: Raspberry Pi Pico (RP2040), Linux ALSA, Windows MIDI Services

1 files changed, 14 insertions, 0 deletions

diff --git a/src/device/usbd.c b/src/device/usbd.c
index 0e58f70bf..55ad330c1 100644
--- a/src/device/usbd.c
+++ b/src/device/usbd.c
@@ -254,6 +254,20 @@ static const usbd_class_driver_t _usbd_driver[] = {
     },
     #endif
 
+    #if CFG_TUD_MIDI2
+    {
+        .name             = DRIVER_NAME("MIDI2"),
+        .init             = midi2d_init,
+        .deinit           = midi2d_deinit,
+        .open             = midi2d_open,
+        .reset            = midi2d_reset,
+        .control_xfer_cb  = midi2d_control_xfer_cb,
+        .xfer_cb          = midi2d_xfer_cb,
+        .xfer_isr         = NULL,
+        .sof              = NULL
+    },
+    #endif
+
     #if CFG_TUD_VENDOR
     {
         .name             = DRIVER_NAME("VENDOR"),