x86: i8259: export legacy_pic symbol

The classic PC rtc-coms driver has a workaround for broken ACPI device
nodes for it which lack an irq resource. This workaround used to
unconditionally hardcode the irq to 8 in these cases.

This was causing irq conflict problems on systems without a legacy-pic
so a recent patch added an if (nr_legacy_irqs()) guard to the
workaround to avoid this irq conflict.

nr_legacy_irqs() uses the legacy_pic symbol under the hood causing
an undefined symbol error if the rtc-cmos code is build as a module.

This commit exports the legacy_pic symbol to fix this.

Cc: rtc-linux@googlegroups.com
Cc: alexandre.belloni@free-electrons.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>