soc: ti: Add MSI domain bus support for Interrupt Aggregator

With the system coprocessor managing the range allocation of the
inputs to Interrupt Aggregator, it is difficult to represent
the device IRQs from DT.

The suggestion is to use MSI in such cases where devices wants
to allocate and group interrupts dynamically.

Create a MSI domain bus layer that allocates and frees MSIs for
a device.

APIs that are implemented:
- ti_sci_inta_msi_create_irq_domain() that creates a MSI domain
- ti_sci_inta_msi_domain_alloc_irqs() that creates MSIs for the
  specified device and resource.
- ti_sci_inta_msi_domain_free_irqs() frees the irqs attached to the device.
- ti_sci_inta_msi_get_virq() for getting the virq attached to a specific event.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

include/linux/msi.h

@@ -47,6 +47,14 @@ struct fsl_mc_msi_desc {
 	u16				msi_index;
 };
 
+/**
+ * ti_sci_inta_msi_desc - TISCI based INTA specific msi descriptor data
+ * @dev_index: TISCI device index
+ */
+struct ti_sci_inta_msi_desc {
+	u16	dev_index;
+};
+
 /**
  * struct msi_desc - Descriptor structure for MSI based interrupts
  * @list:	List head for management
@@ -68,6 +76,7 @@ struct fsl_mc_msi_desc {
  * @mask_base:	[PCI MSI-X] Mask register base address
  * @platform:	[platform]  Platform device specific msi descriptor data
  * @fsl_mc:	[fsl-mc]    FSL MC device specific msi descriptor data
+ * @inta:	[INTA]	    TISCI based INTA specific msi descriptor data
  */
 struct msi_desc {
 	/* Shared device/bus type independent data */
@@ -106,6 +115,7 @@ struct msi_desc {
 		 */
 		struct platform_msi_desc platform;
 		struct fsl_mc_msi_desc fsl_mc;
+		struct ti_sci_inta_msi_desc inta;
 	};
 };