powerpc: Remove all usages of NO_IRQ

NO_IRQ has been == 0 on powerpc for just over ten years (since commit
0ebfff1491ef ("[POWERPC] Add new interrupt mapping core and change
platforms to use it")). It's also 0 on most other arches.

Although it's fairly harmless, every now and then it causes confusion
when a driver is built on powerpc and another arch which doesn't define
NO_IRQ. There's at least 6 definitions of NO_IRQ in drivers/, at least
some of which are to work around that problem.

So we'd like to remove it. This is fairly trivial in the arch code, we
just convert:

    if (irq == NO_IRQ)	to	if (!irq)
    if (irq != NO_IRQ)	to	if (irq)
    irq = NO_IRQ;	to	irq = 0;
    return NO_IRQ;	to	return 0;

And a few other odd cases as well.

At least for now we keep the #define NO_IRQ, because there is driver
code that uses NO_IRQ and the fixes to remove those will go via other
trees.

Note we also change some occurrences in PPC sound drivers, drivers/ps3,
and drivers/macintosh.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/sound/ppc/tumbler.c b/sound/ppc/tumbler.c
index c8fafba..58ee808 100644
--- a/sound/ppc/tumbler.c
+++ b/sound/ppc/tumbler.c
@@ -1303,19 +1303,19 @@
 				    &mix->line_mute, 1);
 	irq = tumbler_find_device("headphone-detect",
 				  NULL, &mix->hp_detect, 0);
-	if (irq <= NO_IRQ)
+	if (irq <= 0)
 		irq = tumbler_find_device("headphone-detect",
 					  NULL, &mix->hp_detect, 1);
-	if (irq <= NO_IRQ)
+	if (irq <= 0)
 		irq = tumbler_find_device("keywest-gpio15",
 					  NULL, &mix->hp_detect, 1);
 	mix->headphone_irq = irq;
  	irq = tumbler_find_device("line-output-detect",
 				  NULL, &mix->line_detect, 0);
- 	if (irq <= NO_IRQ)
+	if (irq <= 0)
 		irq = tumbler_find_device("line-output-detect",
 					  NULL, &mix->line_detect, 1);
-	if (IS_G4DA && irq <= NO_IRQ)
+	if (IS_G4DA && irq <= 0)
 		irq = tumbler_find_device("keywest-gpio16",
 					  NULL, &mix->line_detect, 1);
 	mix->lineout_irq = irq;