genirq: export handle_edge_irq() and irq_to_desc()

Export handle_edge_irq() and irq_to_desc() to modules to allow them to
do things such as

	__irq_set_handler_locked(...., handle_edge_irq);

This fixes

	ERROR: "handle_edge_irq" [drivers/gpio/gpio-pch.ko] undefined!
	ERROR: "irq_to_desc" [drivers/gpio/gpio-pch.ko] undefined!

when gpio-pch is being built as a module.

This was introduced by commit df9541a6 ("gpio: pch9: Use proper flow
type handlers") that added

	__irq_set_handler_locked(d->irq, handle_edge_irq);

but handle_edge_irq() was not exported for modules (and inlined
__irq_set_handler_locked() requires irq_to_desc() exported as well)

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>