ARM: pxa: fix broken isa interrupts for zeus and viper

Commit "ARM: pxa: arbitrarily set first interrupt number" broke viper
and zeus boards which still refer to PXA_ISA_IRQ() macro. Redefine
the macro, which declares the legacy interrupts from 0 to 15.
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/mach-pxa/include/mach/irqs.h

@@ -14,6 +14,7 @@
 
 #include <asm/irq.h>
 
+#define PXA_ISA_IRQ(x)	(x)
 #define PXA_IRQ(x)	(NR_IRQS_LEGACY + (x))
 
 #define IRQ_SSP3	PXA_IRQ(0)	/* SSP3 service request */