ACPI: Introduce acpi_os_get_iomem()

Introduce function acpi_os_get_iomem() that may be used by its callers
to get a reference to an ACPI iomap.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/include/linux/acpi_io.h b/include/linux/acpi_io.h
index 28a3ae2..4afd710 100644
--- a/include/linux/acpi_io.h
+++ b/include/linux/acpi_io.h
@@ -10,4 +10,6 @@
        return ioremap_cache(phys, size);
 }
 
+void __iomem *acpi_os_get_iomem(acpi_physical_address phys, unsigned int size);
+
 #endif