Add optional interrupt support to the da9210 regulator driver, to handle
over-current, under- and over-voltage, and over-temperature events.

Only the interrupt sources for which we handle events are unmasked, to
avoid interrupts we cannot handle.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>