usb: udc: Add trace event for usb_gadget_set_state

While the userspace program can be notified of gadget state changes,
timing issue can lead to missed transitions when reading the state
value.

Introduce a trace event for usb_gadget_set_state to reliably track state
transitions.

Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://lore.kernel.org/r/20250818082722.2952867-1-khtsai@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>