genirq: Expand doc for PENDING and REPLAY flags

Adding a bit more info about what the flags are used for may help future
code readers.
Signed-off-by: James Gowans <jgowans@amazon.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Liao Chang <liaochang1@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230608120021.3273400-2-jgowans@amazon.com

kernel/irq/internals.h

@@ -47,9 +47,12 @@ enum {
  *				  detection
  * IRQS_POLL_INPROGRESS		- polling in progress
  * IRQS_ONESHOT			- irq is not unmasked in primary handler
- * IRQS_REPLAY			- irq is replayed
+ * IRQS_REPLAY			- irq has been resent and will not be resent
+ * 				  again until the handler has run and cleared
+ * 				  this flag.
  * IRQS_WAITING			- irq is waiting
- * IRQS_PENDING			- irq is pending and replayed later
+ * IRQS_PENDING			- irq needs to be resent and should be resent
+ * 				  at the next available opportunity.
  * IRQS_SUSPENDED		- irq is suspended
  * IRQS_NMI			- irq line is used to deliver NMIs
  * IRQS_SYSFS			- descriptor has been added to sysfs