These functions might be called from modules as well so make sure
they are exported.

In addition, implement empty version of acpi_unregister_gsi() and
remove the one from pci_irq.c.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: NH. Peter Anvin <hpa@zytor.com>
Acked-by: NTony Luck <tony.luck@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>