[IA64] add driver for ACPI methods to call native firmware

This driver for HPQ5001 devices installs a global ACPI OpRegion handler.
AML methods can use this OpRegion to call native firmware entry points.

ACPI does not define a mechanism for AML methods to call native firmware
interfaces such as PAL or SAL.  This OpRegion handler adds such a mechanism.
After the handler is installed, an AML method can call native firmware by
storing the arguments and firmware entry point to specific offsets in the
OpRegion.  When AML reads the "return value" offset from the OpRegion, this
handler loads up the arguments, makes the firmware call, and returns the
result.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>