usb: usb251xb: use modern PM macros

Use the modern PM macros for the suspend and resume functions to be
automatically dropped by the compiler when CONFIG_PM or
CONFIG_PM_SLEEP are disabled, without having to use __maybe_unused.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Richard Leitner <richard.leitner@linux.dev>
Link: https://lore.kernel.org/r/20250825234509.1041-3-jszhang@kernel.org


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