Input: gpio_keys - switch to using request_any_context_irq

The driver does not require hardirq context and can work with threaded
interrupts as well, so let's switch to request_any_context_irq which
will select the context that is available for us.

Signed-off-by: Philippe Langlais <philippe.langlais@stericsson.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>