usb: gadget: udc: atmel: convert to platform driver

The driver won't probe on a LAN9668 because the pinctrl driver isn't
ready yet. Probe deferral is not supported because the init section
is already discarded. With fw_devlink enabled, the probe won't even
be called. Convert the driver to a proper platform driver.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220705131951.1388968-2-michael@walle.cc


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