Instead of using custom caching, this switches to regmap based
caching. Before the conversion the debugfs file used uncached
values, so that it was easily possible to see power-loss related
problems. The new code will check and recover at this place.

The patch will also ensure, that irqs are not cleared by checking
register status in debugfs.
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>