gpio: omap: Convert to immutable irq_chip

gpio: omap: Convert to immutable irq_chip

Convert the driver to immutable irq-chip with a bit of
intuition.

This driver require some special care: .irq_ack() was copied
from dummy_irq_chip where it was defined as noop. This only
makes sense if using handle_edge_irq() that will unconditionally
call .irq_ack() to avoid a crash, but this driver is not ever
using handle_edge_irq() so just avoid assigning .irq_ack().

A separate chip had to be created for the non-wakeup instance.

Cc: Marc Zyngier <maz@kernel.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>