acpi: remove final __acpi_map_table mapping before setting acpi_gbl_permanent_mmap

On x86, __acpi_map_table uses early_ioremap() to create the mapping,
replacing the previous mapping with a new one.  Once enough of the
kernel is up an running it switches to using normal ioremap().  At
that point, we need to clean up the final mapping to avoid a warning
from the early_ioremap subsystem.

This can be removed after all the instances in the ACPI code are fixed
that rely on early-ioremap's implicit overmapping of previously
mapped tables.

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>