cachyos-bugreport: add xHCI debug information section

[VECTORG99]

Summary

Add a new get_xhci_debug() function and a corresponding section to cachyos-bugreport.sh, inserted between the scheduler block and the full dmesg section.

This collects targeted, privacy-conscious xHCI/USB diagnostics — controller listing, xHCI/USB lines from dmesg, and a names-and-sizes-only listing of the xHCI debugfs tree — so users can include USB/xHCI context in bug reports without pasting a full dmesg or debugfs data dumps.

What it does

• Detects an xHCI controller via /proc/modules; prints "No xHCI controller found" and exits gracefully otherwise.
• Lists USB controllers with lspci -nn.
• Greps dmesg for xhci|xHC|new USB device lines.
• Lists the debugfs xHCI tree (/sys/kernel/debug/usb/xhci) with file names and sizes only — no file contents, no dynamic-debug writes, no register dumps.
• Falls back gracefully if lspci or debugfs are unavailable.

Privacy / safety

The section is intentionally conservative:

• Only paths + byte sizes are reported from debugfs; no file contents are dumped.
• No writes to debugfs, no echo to dynamic-debug control files, no kernel tracing enabled.
• All greps use || true/|| echo fallbacks so the section never fails the script under set -euo pipefail.