x86: always explicitly map acpi memory

Always map acpi tables, rather than assuming we can use the normal
linear mapping to access the acpi tables.  This is necessary in a
virtual environment where the linear mappings are to pseudo-physical
memory, but the acpi tables exist at a real physical address.  It
doesn't hurt to map in the normal non-virtual case, so just do it
unconditionally.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>