usb: gadget: CDC ACM: call usb_gadget_initialize

To actually use the gadget the peripheral driver must be probed and we
must call g_dnl_clear_detach(). Otherwise acm_stdio_start() will always
fail to find a UDC on DT platforms.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Link: https://lore.kernel.org/r/20240320-b4-qcom-usb-v4-3-41be480172e1@linaro.org


Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>