irqdomain: Fix the kernel-doc and plug it into Documentation

There were several undocumented fields in structs irq_domain_ops and
irq_domain_info. Document them.

irq_domain_ops::revmap_size contained "[]" in the description, which is not
allowed in sphinx. Remove that.

Finally, plug the whole header (irqdomain.h) into genericirq.rst, so that
the docs is autogenerated and hyperlinks to these structure are created.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20240712064148.157040-1-jirislaby@kernel.org