firmware: add nowarn variant of request_firmware_nowait()

Device drivers with optional firmware may still want to use the
asynchronous firmware loading interface. To avoid printing a
warning into the kernel log when the optional firmware is
absent, add a nowarn variant of this interface.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20240516102532.213874-1-l.stach@pengutronix.de


Signed-off-by: Vinod Koul <vkoul@kernel.org>