hw/sysbus.h: Increase maximum number of device IRQs.

Samsung exynos4210 Interrupt Combiner needs 512 IRQ sources.
Signed-off-by: NEvgeny Voevodin <e.voevodin@samsung.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndrzej Zaborowski <andrew.zaborowski@intel.com>

hw/sysbus.h

@@ -8,7 +8,7 @@
 
 #define QDEV_MAX_MMIO 32
 #define QDEV_MAX_PIO 32
-#define QDEV_MAX_IRQ 256
+#define QDEV_MAX_IRQ 512
 
 typedef struct SysBusDevice SysBusDevice;