ACPI / tables: table upgrade: use cacheable map for tables

The new memory allocated in acpi_table_initrd_init() is used to
copy the upgraded tables to it.  So it should be mapped with
early_memunmap() instead of early_ioremap().

This is critical for ARM.

Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Acked-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>