[POWERPC] i8259: Add disable method

Since commit 76d21601, the NE2000 card
is not working anymore on PPC and POWERPC and produces WATCHDOG
timeouts.

The patch below fixes that the same way it has been done on x86, x86_64
and MIPS.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/sysdev/i8259.c

@@ -137,6 +137,7 @@ static void i8259_unmask_irq(unsigned int irq_nr)
 static struct irq_chip i8259_pic = {
 	.typename	= " i8259    ",
 	.mask		= i8259_mask_irq,
+	.disable	= i8259_mask_irq,
 	.unmask		= i8259_unmask_irq,
 	.mask_ack	= i8259_mask_and_ack_irq,
 };

arch/ppc/syslib/i8259.c

@@ -127,6 +127,7 @@ static void i8259_unmask_irq(unsigned int irq_nr)
 static struct irq_chip i8259_pic = {
 	.typename	= " i8259    ",
 	.mask		= i8259_mask_irq,
+	.disable	= i8259_mask_irq,
 	.unmask		= i8259_unmask_irq,
 	.mask_ack	= i8259_mask_and_ack_irq,
 };