acpi: add some missing section markers

early_acpi_os_unmap_memory() is an __init function, and
acpi_os_unmap_memory() is allowed to access an __init function
until acpi_gbl_permanent_mmap is set up.

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