mini-os: respect memory map when ballooning up

mini-os: respect memory map when ballooning up

Today Mini-OS won't look at the memory map when ballooning up. This can
result in problems for PVH domains with more than 4 GB of RAM, as
ballooning will happily run into the ACPI area.

Fix that by adding only pages being marked as RAM in the memory map and
by distinguishing between the current number of RAM pages and the first
unallocated page.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>