[ARM] 3918/1: ixp4xx irq-chip rework

This is a rework of the ixp4xx irq_chip implementation.  The use of
two irq_chip structures and potentially switching between them is a
violation of the intended use of the IRQ framework.  The current
implementation does not work with current in-kernel spinlock debugging
or lockdep due to lock recursion problems caused by calling
set_irq_chip/handler from within the chip's set_irq_type().

This patch goes back to using one irq_chip structure and handling the
differences between edge/level, normal/GPIO interrupts inside the
ack/mask/unmask routines themselves.

Signed-off-by: Kevin Hilman <khilman@mvista.com>
Signed-off-by: Deepak Saxena <dsaxena@mvista.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>