regmap-irq cleanups and refactoring

Merge series from Aidan MacDonald <aidanmacdonald.0x0@gmail.com>:

This series is an attempt at cleaning up the regmap-irq API in order
to simplify things and consolidate existing features, while at the
same time generalizing it to support a wider range of hardware.

There is a new system for IRQ type configuration, some tweaks to
unmask registers so they're more intuitive and useful, and a new
callback for calculating register addresses. There's also a few
minor code cleanups in here.

In v2 I've taken the approach of adding new features and deprecating
existing ones rather than removing them aggressively. Warnings will
be issued for any drivers that use deprecated features, but they'll
otherwise continue to function normally.

One important caveat: not all of these changes are tested beyond
compile testing, since I don't have hardware to exercise all of
the features.