x86/dom0: add extra RAM regions as UNUSABLE for PVH memory map

x86/dom0: add extra RAM regions as UNUSABLE for PVH memory map

When running as PVH Dom0 the native memory map is used in order to
craft a tailored memory map for Dom0 taking into account it's memory
limit.

Dom0 memory is always going to be smaller than the total amount
of memory present on the host, so in order to prevent Dom0 from
relocating PCI BARs over RAM regions mark all the RAM regions not
available to Dom0 as UNUSABLE in the memory map.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>