irqchip/ls-scfg-msi: Map MSIs in the iommu

Add the required iommu_dma_map_msi_msg() when composing the MSI message,
otherwise the interrupts will not work.

Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: jason@lakedaemon.net
Cc: marc.zyngier@arm.com
Cc: zhiqiang.hou@nxp.com
Cc: minghuan.lian@nxp.com
Link: https://lkml.kernel.org/r/20180605122727.12831-1-laurentiu.tudor@nxp.com