regmap-irq: make it possible to add irq_chip do a specific device node

Add a new function regmap_add_irq_chip_np() with its corresponding
devm_regmap_add_irq_chip_np() variant. Sometimes one want to register
the IRQ domain on a different device node that the one of the regmap
node. For example when using a MFD where there are different interrupt
controllers and particularly for the generic regmap gpio_chip/irq_chip
driver. In this case it is not desireable to have the IRQ domain on
the parent node.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20200402203656.27047-5-michael@walle.cc
Signed-off-by: Mark Brown <broonie@kernel.org>