Allocate a userspace buffer for older userspaces. Also eliminate phys_mem
buffer. The memset() in kvmctl really kills initial memory usage but swapping
works even with old userspaces.
A side effect is that maximum guest side is reduced for older userspace on
i386.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>