virtio: Add virtio-over-ivshmem transport driver

This provides a virtio transport driver over the Inter-VM shared memory
device as found in QEMU and the Jailhouse hypervisor.

...

Note: Specification work for both ivshmem and the virtio transport is
ongoing, so details may still change.

Acked-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

drivers/virtio/Kconfig

@@ -95,4 +95,14 @@ config VIRTIO_MMIO_CMDLINE_DEVICES
 
 	 If unsure, say 'N'.
 
+config VIRTIO_IVSHMEM
+	tristate "Driver for ivshmem-based virtio front-end devices"
+	depends on PCI && !HIGHMEM
+	select VIRTIO
+	---help---
+	  This provides virtio front-end devices via ivshmem shared memory
+	  devices.
+
+	  If unsure, say 'N'.
+
 endif # VIRTIO_MENU

drivers/virtio/Makefile

@@ -4,5 +4,6 @@ obj-$(CONFIG_VIRTIO_MMIO) += virtio_mmio.o
 obj-$(CONFIG_VIRTIO_PCI) += virtio_pci.o
 virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
 virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
+obj-$(CONFIG_VIRTIO_IVSHMEM) += virtio_ivshmem.o
 obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
 obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o