MLK-21194 rpmsg: imx_rpmsg: clear pending partition reboot irq status

Clear pending interrupt status of partition reboot during rpmsg
driver probe to avoid to unregister/register virtio device again.

Tested-by: Clark Wang <xiaoning.wang@nxp.com>
Reviewed-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Fugang Duan <fugang.duan@nxp.com>