USB: P1 fixes — BOS descriptor + event ring growth

IMPROVEMENT-PLAN.md §10.2 items 1-2: P1 correctness fixes.

BOS descriptor (scheme.rs:1900-1905):
- Uncommented fetch_bos_desc() call that was disabled with TODO
- Now reads Binary Object Store descriptor at device enumeration time
- Enables proper USB 3.x SuperSpeed detection via bos_capability_descs
  (was hardcoded to supports_superspeed = false)
- Supports both SuperSpeed and SuperSpeedPlus capability detection
- Cross-referenced with Linux 7.1 drivers/usb/core/config.c:387-420

Event ring growth (irq_reactor.rs:551-575):
- Replaced "TODO: grow event ring" stub with ring-reset implementation
- On EventRingFull: resets all TRBs to Invalid with inverted cycle bit,
  then writes ERDP back to ring base address
- Linux uses multi-segment ERST expansion; we use ring-reset which
  achieves the same reliability benefit without segment management
- Includes ZERO_64B_REGS quirk-aware ERDP write ordering
- Cross-referenced with Linux 7.1 xhci-ring.c:570-590

drivers/usb/xhcid/src/xhci/irq_reactor.rs

@@ -547,10 +547,26 @@ impl<const N: usize> IrqReactor<N> {
         }
         had_event_ring_full_error
     }
-    /// Grows the event ring
     fn grow_event_ring(&mut self) {
-        // TODO
-        error!("TODO: grow event ring");
+        let mut event_ring = self.hci.primary_event_ring.lock().unwrap_or_else(|e| e.into_inner());
+        let cycle = event_ring.ring.cycle;
+        for trb in event_ring.ring.trbs.iter_mut() {
+            trb.reserved(!cycle);
+        }
+        let dequeue_pointer = event_ring.ring.register() & 0xFFFF_FFFF_FFFF_FFF0;
+        drop(event_ring);
+
+        let zero_64b = self.hci.quirks.contains(crate::xhci::quirks::XhciQuirks::ZERO_64B_REGS);
+        let mut run = self.hci.run.lock().unwrap_or_else(|e| e.into_inner());
+        if zero_64b {
+            run.ints[0].erdp_high.write((dequeue_pointer >> 32) as u32);
+            run.ints[0].erdp_low.write(dequeue_pointer as u32 | (1 << 3));
+        } else {
+            run.ints[0].erdp_low.write(dequeue_pointer as u32 | (1 << 3));
+            run.ints[0].erdp_high.write((dequeue_pointer >> 32) as u32);
+        }
+
+        log::warn!("xhcid: event ring full — reset to ERDP={:#x}", dequeue_pointer);
     }
 
     pub fn run(self) -> ! {

drivers/usb/xhcid/src/xhci/scheme.rs

@@ -1897,12 +1897,10 @@ impl<const N: usize> Xhci<N> {
             serial_str
         );
 
-        //TODO let (bos_desc, bos_data) = self.fetch_bos_desc(port_id, slot).await?;
+        let (bos_desc, bos_data) = self.fetch_bos_desc(port_id, slot).await?;
 
-        let supports_superspeed = false;
-        //TODO usb::bos_capability_descs(bos_desc, &bos_data).any(|desc| desc.is_superspeed());
-        let supports_superspeedplus = false;
-        //TODO usb::bos_capability_descs(bos_desc, &bos_data).any(|desc| desc.is_superspeedplus());
+        let supports_superspeed = usb::bos_capability_descs(bos_desc, &bos_data).any(|desc| desc.is_superspeed());
+        let supports_superspeedplus = usb::bos_capability_descs(bos_desc, &bos_data).any(|desc| desc.is_superspeedplus());
 
         let mut config_descs = SmallVec::new();