genirq/msi: Create msi_api.h

Create a API header for MSI specific functions which are relevant to device
drivers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221124230313.632679220@linutronix.de

include/linux/msi_api.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef LINUX_MSI_API_H
+#define LINUX_MSI_API_H
+
+/*
+ * APIs which are relevant for device driver code for allocating and
+ * freeing MSI interrupts and querying the associations between
+ * hardware/software MSI indices and the Linux interrupt number.
+ */
+
+struct device;
+
+unsigned int msi_get_virq(struct device *dev, unsigned int index);
+
+#endif