irqchip: Add Layerscape SCFG MSI controller support

Some kind of Freescale Layerscape SoC provides a MSI
implementation which uses two SCFG registers MSIIR and
MSIR to support 32 MSI interrupts for each PCIe controller.
The patch is to support it.

Signed-off-by: Minghuan Lian <Minghuan.Lian@nxp.com>
Tested-by: Alexander Stein <alexander.stein@systec-electronic.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

drivers/irqchip/Kconfig

@@ -246,5 +246,10 @@ config MVEBU_ODMI
 	bool
 	select GENERIC_MSI_IRQ_DOMAIN
 
+config LS_SCFG_MSI
+	def_bool y if SOC_LS1021A || ARCH_LAYERSCAPE
+	depends on PCI && PCI_MSI
+	select PCI_MSI_IRQ_DOMAIN
+
 config PARTITION_PERCPU
 	bool