gpio: lock adnp IRQs when enabling them

This uses the new API for tagging GPIO lines as in use by
IRQs. This enforces a few semantic checks on how the underlying
GPIO line is used.

Only compile tested on the lpc32xx.

ChangeLog v2->v3:
- Switch to using the startup()/shutdown() callbacks again.
  Still satisfy the mask/unmask semantics.
ChangeLog v1->v2:
- Use the .enable() callback from the irq_chip
- Call .unmask() from the .enable() callback to satisfy semantics.

Cc: Lars Poeschel <poeschel@lemonage.de>
Cc: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>