hw: misc, add educational driver

I am using qemu for teaching the Linux kernel at our university. I
wrote a simple PCI device that can answer to writes/reads, generate
interrupts and perform DMA. As I am dragging it locally over 2 years,
I am sending it to you now.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
[Fix 32-bit compilation. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>