omap: fix false lockdep warnings

Remove false lockdep warnings about lock recursion when declaring
IRQs as being wake-capable, by marking putting GPIO irq_desc locks
into their own class.

(Thanks to Peter Zijlstra for helping track down such a small
fix to this problem.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Tony Lindgren <tony@atomide.com>