firmware: imx: make sure MU irq can wake up system from suspend mode

IRQF_NO_SUSPEND flag is set for MU IRQ of IPC work, but with this
flag set, IRQD_WAKEUP_ARMED flag will NOT be set during
suspend_device_irq() phase, then when MU IRQ arrives, it will NOT
wake up system from suspend.

To fix this issue, pm_system_wakeup() is called in general MU IRQ
handler to make sure system can be waked up when MU IRQ arrives.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>