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/drivers/macintosh/via-pmu.c b/drivers/macintosh/via-pmu.c
index f8b6d14..91081dc 100644
--- a/drivers/macintosh/via-pmu.c
+++ b/drivers/macintosh/via-pmu.c
@@ -145,7 +145,7 @@
 static int pmu_has_adb;
 static struct device_node *gpio_node;
 static unsigned char __iomem *gpio_reg;
-static int gpio_irq = NO_IRQ;
+static int gpio_irq = 0;
 static int gpio_irq_enabled = -1;
 static volatile int pmu_suspended;
 static spinlock_t pmu_lock;
@@ -402,7 +402,7 @@
 	batt_req.complete = 1;
 
 	irq = irq_of_parse_and_map(vias, 0);
-	if (irq == NO_IRQ) {
+	if (!irq) {
 		printk(KERN_ERR "via-pmu: can't map interrupt\n");
 		return -ENODEV;
 	}
@@ -424,7 +424,7 @@
 		if (gpio_node)
 			gpio_irq = irq_of_parse_and_map(gpio_node, 0);
 
-		if (gpio_irq != NO_IRQ) {
+		if (gpio_irq) {
 			if (request_irq(gpio_irq, gpio1_interrupt,
 					IRQF_NO_SUSPEND, "GPIO1 ADB",
 					(void *)0))