Rework default hwirq handler so there is no confusion on which pic to eoi.

Introduce two default handlers (hwpic1 and hwpic2) and register them
    accordingly.  This ensures the proper pic always gets an eoi.
Also, use DEBUG_ISR_hwpic1/2 to determine debugging level.
diff --git a/src/post.c b/src/post.c
index 77c7797..b286826 100644
--- a/src/post.c
+++ b/src/post.c
@@ -48,9 +48,9 @@
     // Initialize all hw vectors to a default hw handler.
     for (i=0x08; i<=0x0f; i++)
-        set_irq(i, entry_hwirq);
+        set_irq(i, entry_hwpic1);
     for (i=0x70; i<=0x77; i++)
-        set_irq(i, entry_hwirq);
+        set_irq(i, entry_hwpic2);
     // Initialize software handlers.
     set_irq(0x10, entry_10);