Based on the crates.io synopsys-usb-otg 0.4.0 package, SHA-256
`e948d523b316939545d8b21a48c27aef150ce25321b9f95ff7978647a806a6fe`.
Upstream source and MIT license are retained.

The local change serializes USB operations without masking unrelated interrupts
while hardware completes. F722 full-speed reset and FIFO waits have a clock deadline and
a finite polling limit. Failure permanently aborts the peripheral until restart.
The platform supplies the clock, limits and bounded abort operation.

From `firmware/`, run `cargo test -p platform-stm32f7
-p synopsys-usb-otg --lib --locked --offline`. These tests exercise the
production bus against register storage; they do not measure hardware. Upstream
generated RAL doctests refer to another crate and are not included in this gate.