um: add PCI over virtio emulation driver

To support testing of PCI/PCIe drivers in UML, add a PCI bus
support driver. This driver uses virtio, which in UML is really
just vhost-user, to talk to devices, and adds the devices to
the virtual PCI bus in the system.

Since virtio already allows DMA/bus mastering this really isn't
all that hard, of course we need the logic_iomem infrastructure
that was added by a previous patch.

The protocol to talk to the device is has a few fairly simple
messages for reading to/writing from config and IO spaces, and
messages for the device to send the various interrupts (INT#,
MSI/MSI-X and while suspended PME#).

Note that currently no offical virtio device ID is assigned for
this protocol, as a consequence this patch requires defining it
in the Kconfig, with a default that makes the driver refuse to
work at all.

Finally, in order to add support for MSI/MSI-X interrupts, some
small changes are needed in the UML IRQ code, it needs to have
more interrupts, changing NR_IRQS from 64 to 128 if this driver
is enabled, but not actually use them for anything so that the
generic IRQ domain/MSI infrastructure can allocate IRQ numbers.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/io.h

@@ -3,16 +3,23 @@
 #define _ASM_UM_IO_H
 #include <linux/types.h>
 
+/* get emulated iomem (if desired) */
+#include <asm-generic/logic_io.h>
+
+#ifndef ioremap
 #define ioremap ioremap
 static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
 {
 	return NULL;
 }
+#endif /* ioremap */
 
+#ifndef iounmap
 #define iounmap iounmap
 static inline void iounmap(void __iomem *addr)
 {
 }
+#endif /* iounmap */
 
 #include <asm-generic/io.h>