microblaze: Change NO_IRQ to 0

microblaze: Change NO_IRQ to 0

As has been discussed many times[1], Using NO_IRQ set to anything other
than 0 is bug waiting to happen since many drivers follow the pattern
"if (!irq)" for testing whether or not an irq has been set.

This patch changes the Microblaze NO_IRQ setting from -1 to 0 to bring
it in line with most of the rest of the kernel.  It also prepares for
Microblaze eventually supporting multiple interrupt controllers by
breaking the assumption that hwirq# == Linux IRQ#.  The Linux IRQ
number is just a cookie with no guarantee of a direct relationship
with the hardware irq arrangement.

At this point, Microblaze interrupt handling only supports only one
instance of one kind of interrupt controller (xilinx_intc).  This change
shouldn't affect any architecture code outside of the interrupt
controller driver and the irq_of mapping.

Updated to 3.2 and to use irq_data.hwirq by Rob Herring.
Tested and fixed by Michal Simek.

[1] http://lkml.org/lkml/2005/11/21/221

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>