regulator: da9211: add cache_type

Add regmap_cache to reduce wakeups events of interrupt if regulator is
accessed frequently. This results in saving more power.

Suggested-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Link: https://lore.kernel.org/r/20200812133101.2513317-1-hsinyi@chromium.org


Signed-off-by: Mark Brown <broonie@kernel.org>