docs: Add request_irq() documentation

While checking the results of the :c:func: removal, I noticed that there
was no documentation for request_irq(), and request_threaded_irq() was not
mentioned at all.  Add a kerneldoc comment for request_irq() and add
request_threaded_irq() to the list of functions.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/core-api/genericirq.rst

@@ -127,6 +127,8 @@ The high-level Driver API consists of following functions:
 
 -  request_irq()
 
+-  request_threaded_irq()
+
 -  free_irq()
 
 -  disable_irq()

include/linux/interrupt.h

@@ -140,6 +140,19 @@ request_threaded_irq(unsigned int irq, irq_handler_t handler,
 		     irq_handler_t thread_fn,
 		     unsigned long flags, const char *name, void *dev);
 
+/**
+ * request_irq - Add a handler for an interrupt line
+ * @irq:	The interrupt line to allocate
+ * @handler:	Function to be called when the IRQ occurs.
+ *		Primary handler for threaded interrupts
+ *		If NULL, the default primary handler is installed
+ * @flags:	Handling flags
+ * @name:	Name of the device generating this interrupt
+ * @dev:	A cookie passed to the handler function
+ *
+ * This call allocates an interrupt and establishes a handler; see
+ * the documentation for request_threaded_irq() for details.
+ */
 static inline int __must_check
 request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,
 	    const char *name, void *dev)