genirq: Query arch for number of early descriptors

sparse irq sets up NR_IRQS_LEGACY irq descriptors and archs then go
ahead and allocate more.

Use the unused return value of arch_probe_nr_irqs() to let the
architecture return the number of early allocations. Fix up all users.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 096b74d..ef87882 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -214,6 +214,10 @@
  */
 #include <asm/hw_irq.h>
 
+#ifndef NR_IRQS_LEGACY
+# define NR_IRQS_LEGACY 0
+#endif
+
 #ifndef ARCH_IRQ_INIT_FLAGS
 # define ARCH_IRQ_INIT_FLAGS	0
 #endif