ACPI: Add interfaces for ioremapping/iounmapping ACPI registers

Add remapping and unmapping interfaces for ACPI registers that are
backed by memory mapped I/O (MMIO).  These interfaces, along with
the MMIO remapping list, enable accesses of such registers from within
interrupt context.

ACPI Generic Address Structure (GAS) reference (ACPI's fixed/generic
hardware registers use the GAS format):
  ACPI Specification, Revision 4.0, Section 5.2.3.1, "Generic Address
  Structure".

Signed-off-by: Myron Stowe <myron.stowe@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index c227757..7774e6d 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -308,6 +308,9 @@
 					     u32 *mask, u32 req);
 extern void acpi_early_init(void);
 
+int acpi_os_map_generic_address(struct acpi_generic_address *addr);
+void acpi_os_unmap_generic_address(struct acpi_generic_address *addr);
+
 #else	/* !CONFIG_ACPI */
 
 #define acpi_disabled 1