[EMULATORS] Add support for Virtio PCI transport layer.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[EMULATORS] Small fix in calculating dev num in i440fx emulator.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[x86] Add BAR region for XPSM driver.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[x86] Enable emulation of Virtio block device.

Add a Virtio block device using the PCI layer emulation.
The partition is hardcoded to the one used by VMM.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[DOCS][x86] Building Coreboot and FILO

Add documentation on how to build Coreboot and FILO
to be used as guest.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>