irqdomain: Introduce irq_domain_create_simple() API

Linus Walleij pointed out that ird_domain_add_simple() gained
additional functionality and can't be anymore replaced with
a simple conditional. In preparation to upgrade GPIO library
to use fwnode, introduce irq_domain_create_simple() API which is
functional equivalent to the existing irq_domain_add_simple(),
but takes a pointer to the struct fwnode_handle as a parameter.

While at it, amend documentation to mention irq_domain_create_*()
functions where it makes sense.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>