[zircon] Fix XHCI, PHY tuning, and CDC Ethernet issues

This patch fixes various XHCI issues that caused problems
with CDC-Ethernet on certain boards with high-latency interrupts.

The following changes have been made in this patch:

* Add a direct mode for USB URBs to bypass re-assembly
and buffering throughout the pipeline and take the
most "direct" path from an interrupt handler to driver code.

* Enable direct mode for CDC Ethernet TX and RX paths.
* Increase the buffer size used for CDC Ethernet.
* Implement multi-page TRB support in XHCI.
* Increase the size of the transfer and event ring buffers.
* Revert workaround in pack-images.py

CONN-50
ZX-3957

Test: Validate no software-related packet loss in XHCI and
CDC Ethernet drivers on affected boards. Ran additional tests described
in CONN-50.

Change-Id: Ice7429ee63109db67b254488d7127a8bd95394ab
19 files changed
tree: d4a5ba87f7bc323f291af40132c8ac645922ea0a
  1. .clang-format
  2. .clang-tidy
  3. .dir-locals.el
  4. .gitattributes
  5. .gitignore
  6. .gn
  7. AUTHORS
  8. BUILD.gn
  9. CODE_OF_CONDUCT.md
  10. CONTRIBUTING.md
  11. LICENSE
  12. OWNERS
  13. PATENTS
  14. README.md
  15. boards/
  16. build/
  17. buildtools/
  18. bundles/
  19. docs/
  20. examples/
  21. garnet/
  22. infra/
  23. peridot/
  24. products/
  25. rustfmt.toml
  26. scripts/
  27. sdk/
  28. src/
  29. third_party/
  30. tools/
  31. zircon/
README.md

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