remoteproc: imx_rproc: Initialize workqueue earlier

Initialize workqueue before requesting mailbox channel, otherwise if
mailbox interrupt comes before workqueue ready, the imx_rproc_rx_callback
will trigger issue.

Fixes: 2df70620 ("remoteproc: imx_proc: enable virtio/mailbox")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20240719-imx_rproc-v2-3-10d0268c7eb1@nxp.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>