lguest: add MMIO region allocator in example launcher.

This is where we point our PCI BARs, so that we can intercept MMIO
accesses.  We tell the kernel about it so any faults in this area are
directed to us.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --cc tools/lguest/lguest.c
Simple merge