cxgbe(4): Improvements to the slow interrupt handler

* Add a flag to indicate that an INT_CAUSE should not be cleared
  automatically in the generic handler.  This is to ensure correct
  operation of some INT_CAUSEs that are related to each other and must
  be cleared in a certain order.
* Add decode for many more INT_CAUSE registers.

MFC after:	1 week
Sponsored by:	Chelsio Communications

sys/dev/cxgbe/adapter.h

@@ -194,6 +194,7 @@ enum {
 	IHF_CLR_ALL_SET		= (1 << 5),	/* Clear all set bits */
 	IHF_CLR_ALL_UNIGNORED	= (1 << 6),	/* Clear all unignored bits */
 	IHF_RUN_ALL_ACTIONS	= (1 << 7),	/* As if all cause are set */
+	IHF_CLR_DELAYED		= (1 << 9),	/* Cleared in a delayed call */
 };
 
 #define IS_DETACHING(vi)	((vi)->flags & VI_DETACHING)